How to Measure a Boat for Cover Size (2025 Guide)

Measuring a boat for the right cover size is the single most important step you’ll take before making a purchase—and it’s where most boat owners go wrong.

Think about it: you’ve invested thousands, maybe tens of thousands, into your vessel.

Yet a poorly measured cover can undo all your protective efforts in a single storm season.

Water pools in sagging fabric, UV rays sneak through gaps, and wind transforms loose material into sandpaper against your gel coat.

The frustrating part? These problems are completely avoidable.

Boat cover manufacturers provide sizing charts, but they’re only useful if you feed them accurate numbers.

And here’s what catches people off guard—your boat’s factory specifications rarely tell the whole story.

That aftermarket swim platform? The trolling motor you added last summer? The new fish finder mounted on your console?

None of these appear in your owner’s manual, but they absolutely affect which cover will actually fit.

This guide breaks down the professional measurement process into clear, actionable steps.

You’ll learn exactly where to place your tape measure, which dimensions matter most, and how to account for every unique feature on your boat.

Whether you’re shopping for a universal cover, a semi-custom option, or considering a fully tailored solution, the measurement fundamentals remain the same.

By the time you finish reading, you’ll have the confidence to select a cover that fits like it was made specifically for your boat—because in a sense, with the right measurements, it will be.

Let’s start with understanding why getting these numbers right matters so much to your boat’s long-term protection.

Understanding Why Accurate Boat Measurements Matter

The difference between a cover that protects and one that destroys often comes down to a few inches.

That’s not an exaggeration—it’s a reality countless boat owners discover the hard way every season.

The Hidden Costs of Poor-Fitting Covers

A cover that’s too large creates a dangerous situation you might not notice until the damage is done.

Excess fabric catches wind like a sail, flapping violently against your boat’s surface during even moderate breezes.

That constant movement creates friction against your gel coat, hardware, and windshield.

Over time, you’ll see scratches, dull spots, and worn areas appearing in patterns that match the fabric’s movement.

But oversized covers bring another problem: water pooling.

When fabric sags between support points, rainwater and snow collect in low spots.

These pools can weigh dozens of pounds, stretching the cover material and creating permanent deformations.

Eventually, the weight tears through the fabric or—worse—puts enough pressure on your boat’s components to cause structural stress.

« Most boat owners don’t realize that an ill-fitting cover causes more damage annually than leaving a boat completely uncovered in many cases. »

Undersized covers present the opposite problem but with equally frustrating results.

When a cover doesn’t fully reach your boat’s edges, you’re left with exposed areas that:

Absorb direct UV radiation, fading and degrading vinyl, upholstery, and finishes
Collect bird droppings, tree sap, and debris that would otherwise slide off the cover
Allow moisture intrusion during rain, promoting mold and mildew growth
Create entry points for pests seeking shelter in your vessel

Why Manufacturer Sizing Charts Aren’t Enough

Here’s something that surprises many first-time cover buyers: sizing charts vary dramatically between brands.

One manufacturer’s « 18-foot » cover might fit boats measuring 17’6″ to 18’6″.

Another brand’s « 18-foot » option could be designed for 17’0″ to 19’0″.

These overlapping ranges create confusion, and without precise measurements, you’re essentially guessing.

The situation becomes more complex when you consider cover types:

Universal covers fit broad ranges (typically 2-3 foot spans) and rely on adjustable straps and elastic hems to accommodate various hull shapes
Semi-custom covers are designed for specific boat styles with 6-inch sizing increments, requiring more precise measurements
Custom covers are built from exact specifications, meaning every measurement must be accurate to within an inch

At Safeboatz, we’ve seen countless customers struggle with sizing because they relied solely on manufacturer charts without taking their own measurements first.

The Financial Argument for Measuring Right

Let’s talk money, because inaccurate measurements hit your wallet in multiple ways.

Return shipping costs on boat covers often run $30-$75 depending on size and carrier.

That’s money you lose if the first cover doesn’t fit.

Then there’s the depreciation factor.

A boat left partially exposed or damaged by a flapping cover loses resale value faster than a well-protected vessel.

Paint oxidation, cracked vinyl, and weathered hardware are immediate red flags to potential buyers.

Some boat owners go through two or three covers before finding one that fits properly—spending double or triple what a single, correctly-sized cover would have cost.

The math is simple: spending 15 minutes measuring accurately saves hours of frustration and hundreds of dollars in replacement costs.

Your measurements become the foundation for a purchasing decision you’ll live with for years.

Getting them right the first time isn’t just convenient—it’s the smartest investment in your boat’s protection you can make.

Essential Tools and Preparation Before Measuring

Essential tools and preparation before measuring your boat can make the difference between a frustrating afternoon and a quick, accurate process that leads to the perfect cover fit.

Think of it like preparing for a home renovation project—you wouldn’t start tearing down walls without gathering your tools and clearing the workspace first.

Gathering Your Measurement Arsenal

You’ll need a flexible measuring tape that extends at least 25-30 feet—rigid carpenter’s tapes simply won’t cut it when you’re working around curves and hull contours.

Grab a notepad or your smartphone to record measurements immediately, because trust me, you will forget that beam width number by the time you walk back to your computer.

For boats longer than 16 feet, recruit a helper to hold the other end of your tape measure.

Trying to anchor one end with a rock while stretching to the bow is a recipe for inaccurate readings and unnecessary frustration.

Clearing the Deck for Accurate Readings

Before you stretch out that measuring tape, your boat needs to be stripped down to its permanent fixtures:

Remove all loose items from the deck—coolers, tackle boxes, cushions, and gear
Lower or completely remove your bimini top
Take off detachable fishing rod holders
Remove portable electronics and GPS mounts
Clear any temporary accessories like cup holders or phone mounts

Why does this matter so much?

Every item left on deck can skew your measurements or give you a false sense of what clearance your cover actually needs.

Positioning Your Boat Correctly

Your boat should sit on level ground—whether that’s on your trailer in the driveway or at the marina on a level surface.

A tilted boat throws off both length and height measurements in ways that won’t become apparent until you’re wrestling with an ill-fitting cover.

If you’re measuring on a trailer, make sure the trailer itself is level by checking the tongue position.

Proper boat positioning is critical because even a few degrees of tilt can add or subtract inches from your centerline length reading.

Documentation That Saves Time

Before measuring, write down your boat’s make, model, and year.

This information lets you cross-reference your physical measurements against manufacturer specifications—a smart double-check that catches mistakes.

Take photos of any unique features that might affect cover fit:

T-tops and radar arches
Custom windshield configurations
Trolling motor mounts
Extended swim platforms
Aftermarket leaning posts or center console modifications

These photos become invaluable when you’re comparing cover styles online or speaking with customer service representatives about which product suits your specific setup.

How to Measure Centerline Length Correctly

How to measure centerline length correctly is the single most important skill in selecting a boat cover—get this wrong, and nothing else matters.

The centerline length serves as the primary dimension every manufacturer uses to categorize their covers, making precision here absolutely non-negotiable.

Understanding the Centerline Measurement

Your centerline runs straight down the middle of your boat, from the very tip of the bow to the furthest point at the stern.

This is not the same as measuring along the gunwale (the upper edge of the boat’s side), which would give you a longer, inaccurate number due to the hull’s curves.

Picture drawing a straight line through the exact center of your boat if you were looking at it from above—that’s your centerline.

What to Include in Your Length

Here’s where many boat owners make costly mistakes:

Include: Bow pulpits, anchor rollers, integrated swim platforms
Include: Any permanent fixtures that extend the boat’s overall footprint
Exclude: Outboard motors (unless specifically purchasing a motor cover)
Exclude: Trolling motors in the raised position

For boats with extended swim platforms, measure all the way to the platform’s furthest edge—these platforms are part of your boat’s total length and need coverage.

Swim platforms are one of the most commonly overlooked features when measuring, leading to covers that leave the stern exposed to weather damage.

The Proper Technique

Follow this step-by-step process for accurate centerline measurement:

Position yourself at the bow with your measuring tape’s end at the absolute tip
Have your helper walk the tape straight back along the boat’s center
Keep the tape as straight and level as possible—avoid letting it sag
Extend to the stern’s furthest point, excluding the outboard
Record the measurement to the nearest inch
Measure again to verify your reading

That last step isn’t optional—professional marine upholsterers always measure twice because centerline length drives every other decision in the cover selection process.

Rounding Rules That Prevent Headaches

When your measurement lands between whole numbers (like 18 feet 7 inches), always round up to the next foot.

A cover rated for 19 feet will fit your 18’7″ boat properly, while squeezing into an 18-foot cover creates stress points, gaps at corners, and premature fabric failure.

The small amount of extra material from sizing up also improves ventilation underneath the cover, reducing moisture buildup and mold growth.

This « round up » rule applies universally across manufacturers—it’s better to have slight extra fabric that you can secure tightly than to fight against a cover that’s perpetually too short.

Your centerline measurement forms the foundation of your cover purchase, so take your time, double-check your work, and don’t guess when precision takes just a few extra minutes.

Measuring Beam Width and Height Clearance

Measuring beam width accurately is just as critical as getting your centerline length right—it determines whether your boat cover will drape properly or leave gaps that invite water and debris inside.

Finding Your Boat’s True Beam Width

Start by identifying the widest point of your boat, which is typically located near the mid-section of the hull.

Here’s where many boat owners make a costly mistake: they follow the curve of the hull instead of measuring in a straight horizontal line.

Position yourself at the widest point and stretch your measuring tape straight across from one side to the other, keeping it perfectly level.

Don’t let the tape dip down into the cockpit or follow the gunwale’s contour—you need that flat, horizontal measurement.

Measuring beam width at the widest point ensures your cover will accommodate the full breadth of your vessel without stretching or leaving exposed areas.

Don’t Forget Those Extra Inches

Your beam measurement must include everything that extends beyond the hull itself:

Rub rails that protrude from the hull sides
Fender holders mounted along the gunwales
Rod holders or other permanent fishing accessories
Cleats and hardware that stick out from the deck edge

These seemingly small additions can add 2-4 inches to your overall width, and ignoring them means your cover will be stretched too tight across these high points.

Tackling Height Measurements

Height clearance is where things get interesting—and where your intended use really matters.

Measure from either the waterline (if your boat is in the water) or from the trailer base (if stored on land) straight up to the highest fixed point on your vessel.

This might be your:

Windshield top edge
Center console with electronics
T-top or hardtop structure
Radar arch or antenna mount
Leaning post on fishing boats

« The biggest mistake I see is boat owners measuring to the wrong high point—they forget about that GPS unit or spotlight mounted above the windshield. »

Trailering vs. Mooring: Two Different Measurement Strategies

Here’s something that trips up even experienced boaters: the cover you need for trailering down the highway is fundamentally different from one designed for dock storage.

Trailering covers require lower-profile measurements because they need to hug your boat tightly to resist 60+ mph winds.

You’ll want to remove or fold down anything that creates height, and your measurements should reflect that streamlined configuration.

Mooring or storage covers can accommodate your full height because wind exposure is less severe.

These covers often use support poles to create tent-like peaks that shed water and snow effectively.

According to the U.S. Coast Guard Boating Safety Division, proper boat protection is essential year-round, whether you’re storing your vessel at the dock or preparing it for highway trailering.

Take both sets of measurements if you plan to use your cover for multiple purposes—this information will be invaluable when comparing cover options.

Write down your beam width and height figures right next to your centerline length, and you’ll have the complete dimensional profile needed to find your perfect cover match.

Special Considerations for Different Boat Types

Every boat style presents unique measurement challenges that generic instructions simply don’t address—and overlooking these specifics is a guaranteed path to cover frustration.

Bass Boats: More Than Just Length and Width

Bass boats are measurement nightmares in the best way possible because they’re loaded with accessories that affect cover fit.

Your trolling motor mounted on the bow adds significant length and height that standard measurements miss entirely.

Those elevated casting decks create uneven surfaces that require covers with proper support systems to prevent water pooling.

Don’t forget your fish finders, GPS units, and graph screens mounted on the console—measure to the top of these electronics, not just the console itself.

Center Console Boats: The Vertical Challenge

Center consoles are all about height, and underestimating this dimension is incredibly common.

Measure from the deck to the absolute top of your console, including any T-top frames, rocket launchers, or spreader lights mounted above.

Leaning posts often extend higher than the console itself—check this measurement separately.

If you have outriggers, note whether they fold down or remain extended, as this dramatically changes your cover requirements.

Pontoon Boats: Think Platform, Not Hull

Pontoons require a completely different measurement mindset because you’re essentially covering a floating deck rather than a traditional hull.

Measure the full deck length from the front gate to the rear swim platform
Include all railings in your width measurement—they extend well beyond the deck edge
Account for bimini top frames even when the canvas is removed
Note any ski tow bars or speaker towers that add height

Pontoon covers often require semi-custom fitting to accommodate the unique rectangular deck shape and multiple height variations across the platform.

Bowriders: Windshield and Tower Complications

Bowriders seem straightforward until you factor in that wraparound windshield and potential wakeboard tower.

Measure windshield height at its tallest point—usually the center where the two panels meet.

If you have a wakeboard tower, you’ll need to decide: cover over it or around it?

Tower-up covers require significantly more material and height clearance, while tower-down measurements let you use more standard cover options.

Cuddy Cabins and Sailboats: Cabin Height Rules Everything

For cuddy cabins, the cabin roof becomes your primary height concern, overshadowing everything else on the boat.

Measure to the cabin top, not the windshield, and add a few inches for any deck hardware mounted on the cabin roof.

Sailboats present the ultimate measurement split: mast-up covers protect your rigging but cost significantly more and require precise measurements around spreaders and shrouds, while mast-down covers are simpler but require unstepping the mast for every use.

Jet Boats: Don’t Be Fooled by the Stern

Jet boats hide their propulsion system internally, which means the stern looks deceptively simple.

However, that swim platform and jet intake area still need careful measurement because covers must seal properly around these features to prevent water intrusion into the engine compartment.

Document every unique feature with photos—cover manufacturers appreciate this detail when helping you select the right fit.

Matching Your Measurements to Cover Sizing Charts

You’ve got your measurements written down—now comes the moment of truth where those numbers meet manufacturer sizing charts, and this is where attention to detail really pays off.

Why One Sizing Chart Isn’t Enough

Here’s a reality check that surprises most boat owners: a « 19-foot cover » from Brand A might fit completely differently than a « 19-foot cover » from Brand B.

Manufacturers use different measurement standards, fabric allowances, and fit philosophies.

Pull up sizing charts from at least three different cover brands and compare how your measurements align with each one.

You’ll often find that you’re a solid medium in one brand’s lineup but squeezed into a large with another.

Always compare your measurements against multiple manufacturer guides to account for these variations in sizing standards.

Understanding Your Cover Options

The type of cover you’re shopping for determines how precisely your measurements need to match:

Universal covers fit a range (like 17′-19′ boats) but sacrifice precision for versatility
Semi-custom covers offer 6-inch increments, providing much better fit for most boat styles
Custom covers are made to your exact specifications but cost significantly more

If you’re between sizes with semi-custom options, that 6-inch increment becomes your best friend for dialing in proper fit.

At Safeboatz, our covers are designed with precise 6-inch increments to ensure you get that semi-custom fit without the custom price tag.

The Fabric Stretch Factor

Not all cover materials behave the same way once installed on your boat.

Some fabrics—particularly certain polyester blends—have 2-4% stretch built into their weave.

This means a cover that seems slightly small on paper might actually fit perfectly once you work it onto your boat and let the material settle.

However, relying on stretch to compensate for genuinely undersized covers is a recipe for stress points and premature wear.

Use stretch as a bonus, not a crutch.

Support Pole Planning

Large cockpit areas and flat deck sections need support poles to prevent water pooling—and these requirements affect your sizing decision.

Covers designed with integrated support systems may run larger to accommodate pole placement
Adjustable pole kits work better with covers that have some extra material
Too-tight covers won’t allow proper pole positioning for water runoff

The Power of Customer Reviews

Before finalizing your purchase, dig into customer reviews with a specific mission: find people who own your exact boat type.

Search reviews for mentions of your boat’s make and model, and pay attention to comments about fit accuracy.

Pro tip: Reviews mentioning « runs small » or « generous fit » are gold—they tell you whether to adjust your size selection up or down from what the chart suggests.

When in Doubt, Size Up

This is the single most important rule when your measurements land between sizes: always choose the larger option.

A slightly larger cover is dramatically easier to install, allows better air circulation underneath (preventing mildew), and can be cinched down with straps and tie-downs.

A too-small cover, on the other hand, creates constant tension, exposes corners and edges, and often tears at stress points within the first season.

The extra material from sizing up costs nothing compared to replacing a cover that never fit properly in the first place.

Conclusion

Measuring a boat for the right cover size isn’t rocket science, but it does require attention to detail and a systematic approach.

Get it right, and you’ll enjoy years of worry-free protection for your vessel.

Get it wrong, and you’re looking at premature wear, water damage, and the frustration of buying replacement covers every couple of seasons.

The bottom line is this: accurate measurements are the foundation of proper boat protection.

Your centerline length measurement is the most critical number you’ll record.

Take it from bow tip to stern, include those swim platforms and bow pulpits, and always round up when you’re between sizes.

Your beam width measurement at the widest point—including rub rails and permanent fixtures—ensures the cover wraps properly around your hull without leaving gaps or creating stress points.

Height clearance matters too, especially if you’ve got a center console, T-top, or windshield that needs accommodation.

Remember: a cover that’s slightly too large will always outperform one that’s too small.

Every boat type brings its own measurement challenges.

Bass boat owners need to account for trolling motors and casting decks.

Pontoon enthusiasts must measure the full deck including railings.

Center console captains have to factor in leaning posts and console height.

Whatever you’re piloting, taking those extra few minutes to document unique features will save you from costly returns and disappointing fits.

Don’t rely solely on factory specifications either.

Aftermarket accessories, slight manufacturing variations, and years of modifications mean your boat’s actual dimensions might differ from what’s listed in the owner’s manual.

Grab that measuring tape, recruit a helper for larger vessels, and verify everything yourself.

When comparing your measurements to manufacturer sizing charts, understand that semi-custom covers offer tighter 6-inch increments for better fit, while universal covers sacrifice precision for broader compatibility.

Read customer reviews from owners of similar boats, and don’t hesitate to contact manufacturers directly if you’re between sizes or have unusual features.

Your boat represents a significant investment—treat the cover selection process with the same care you’d give any other important purchase decision.

Now you’ve got the knowledge to measure like a pro and choose a cover that truly fits.

FAQ

Should I include my outboard motor in the length measurement?

Generally no—most boat covers are designed to fit around the motor or leave it exposed for ventilation.

Only include motor length if you’re purchasing a full motor cover or the manufacturer specifically instructs otherwise.

Check the cover description carefully, as some styles like tournament covers are specifically designed to accommodate outboard coverage.

What if my boat measurements fall between two cover sizes?

Always size up when you’re caught between options.

A slightly larger cover offers several advantages:

Easier installation and removal
Better air circulation underneath
Less stress on seams and attachment points
Room for slight measurement errors

A too-small cover creates tension that leads to tearing, poor water runoff, and gaps that expose your boat to the elements.

Do I need to measure differently for trailering vs. storage covers?

Yes—the application absolutely affects how you should approach measurements.

Trailering covers need lower profile measurements and tighter fits to resist highway winds at 60+ mph.

Storage or mooring covers can accommodate higher accessories and slightly looser fits since they’re not fighting constant wind pressure.

Many boaters own both types for complete protection in different scenarios.

The BoatUS Foundation offers comprehensive resources on boat maintenance and protection strategies for various storage situations.

How often should I re-measure my boat for a new cover?

Re-measure whenever you make modifications that change your boat’s dimensions.

Common triggers include:

Adding a trolling motor or upgrading to a larger outboard
Installing a swim platform extension
Mounting a radar arch or T-top
Adding permanent rod holders or electronics

Also re-measure if you’re switching between cover types, such as moving from a universal to a semi-custom fit.

Can I use my boat’s factory specifications instead of measuring myself?

Factory specs provide an excellent starting point, but never rely on them exclusively.

Aftermarket accessories, manufacturing variations, and previous owner modifications can all affect actual dimensions.

Verify factory numbers with your own physical measurements—it takes just 10-15 minutes and prevents expensive sizing mistakes.

For premium boat covers designed specifically for 17-22ft boats, check out Safeboatz’s selection of trailerable covers that combine weather protection with a perfect fit.

What’s the difference between centerline length and overall length?

Centerline length runs along the center of your boat from bow to stern—this is what most cover manufacturers use for sizing.

Overall length might include side-mounted accessories or curved gunwale measurements that don’t accurately represent cover requirements.

Stick to centerline measurements for the most accurate cover fit.

Do I need to remove my bimini top before measuring for a cover?

For most standard boat covers, yes—lower or remove the bimini top before taking measurements.

However, if you’re specifically shopping for a bimini-top compatible cover or a cover designed to fit over the raised top, measure with it in the position you’ll actually use during storage.

Always clarify with the manufacturer which scenario their sizing charts assume.

For additional guidance on protecting your vessel year-round, including weather-related considerations, the NOAA Marine Weather Service provides essential forecasting and safety information for boat owners.

How do weather conditions affect my cover selection?

Weather patterns in your area should influence both your measurement approach and cover choice.

Regions with heavy snow loads require covers with steeper pitches and stronger support systems, while areas with high winds need tighter fits and robust tie-down systems.

Coastal boaters face salt spray and UV exposure, demanding marine-grade fabrics with UV inhibitors.

For additional guidance on protecting your vessel through all seasons, download Safeboatz’s free boat protection guide for expert tips on cover selection, storage, and maintenance.