If you measure your hot tub like a lazy Sunday DIY project, you’ll get a cover that almost fits… which is code for: it leaks heat, catches wind, rubs your cabinet, and looks cheap. A replacement cover has two jobs: seal tight and look good! Here’s how to measure it properly, with the same approach used by cover manufacturers.
Before You Touch the Tape Measure, This is What You Need
- A rigid tape measure (not a floppy cloth one)
- A helper (strongly recommended)
- Notepad/phone for notes + photos
- Two straight household items (for corner radius): ruler/yardstick, book edge, cutting board, etc.
Measure the hot tub shell — not the old cover
Old covers warp, sag, and swell. If you measure the cover, you’re doing it wrong.
Rule #1: measure outside edge to outside edge across the top lip of the tub (where the cover sits).
Rule #2: keep the tape straight, flat, and level.
Step 1: Measure Length (Front-to-Back)
Length = front-to-back measurement across the tub.
- Place the tape on the outside edge at the front of the tub.
- Pull it straight to the outside edge at the back.
- Keep the tape flat and level across the top, then write it down.
Step 2: Measure Width (Side-to-Side)
Width = left-to-right measurement across the tub.
- Stand at the front of the spa and identify the left outside edge and right outside edge of the acrylic shell/lip.
- Pull the tape straight across (don’t dip into the water well).
- Keep it level across the top, then record the number.
Step 3: Measure Corner Radius (This Is Where Most People Screw Up)
Corner radius = how rounded the corner is, so the cover matches the tub shape.
If your cover corners are too square: it jams, buckles, and gaps.
Too round: it leaves exposed corners (hello heat loss + rain intrusion).
The clean method (with a framing square)
- Hold the square tight to the outside corner of the tub.
- Measure from the inside corner of the square to the point where the tub’s curve first touches the straight edge.
- That number is your corner radius.
The way to measure it if you don’t have a framing square
- Put two straight edges together in an L shape (90°).
- Press them against the tub corner.
- Measure from the inside “L” corner to where the tub curve first meets the straight edge.
Step 4: Measure Skirt Length (The Flap Below the Cover)
Skirt length = how far the flap hangs down below the top lip of the spa.
This matters more than people think:
- Covers the exposed acrylic shell for a cleaner look
- Helps block wind/rain
- Improves insulation and reduces heat loss (your guide nails this point)
How to measure it properly
- Put the tape at the top lip of the tub (where the cover sits).
- Measure straight down the outside to where you want the skirt to end.
- Record that number.
Note: If your tub has side panels, steps, or a tight cabinet edge, don’t choose a skirt length that will bunch, rub, or snag.
The “Fit Guarantee” Checklist (Don’t Skip These)
To get a bulletproof order, also capture these details (even if your images focus on the big four):
- Shape: square, rectangle, round, or custom
- Hinge/fold direction: which way the cover folds (important for handles + lifter compatibility)
- Cover thickness/taper: our covers are thicker in the center and taper toward the edges (improves runoff + insulation)
- Strap locations: distance from each corner to strap center (only available on custom covers)
The 5 Most Common Measuring Mistakes
Measuring the old cover instead of the tub
Warped cover = warped measurements = warped fit.
-
Measuring inside-to-inside
That guarantees the cover will be too small. -
Letting the tape sag
A sagging tape steals inches and creates gaps. -
Guessing the corner radius
Guessing is how you end up with exposed corners or buckling. -
Only measuring once
One measurement is a guess wearing a disguise.
Quick FAQ
Should I round my measurements?
Use the unit your manufacturer asks for (often to the nearest ½ inch). Don’t “round aggressively” to make numbers look clean, accuracy beats aesthetics.
What if my tub measures slightly differently in multiple spots?
That’s common. Record both numbers and note the variance. A good cover build accounts for real-world tubs, not fantasy-perfect squares.
Does skirt length affect heat retention?
Yes! It reduces wind getting under the cover edge and helps protect the shell edge from weather exposure.
How do I know my corner radius is right?
If you use the square/L-method and measure consistently, you’ll get the true radius. If your numbers vary a lot corner-to-corner, your tub may be asymmetrical; note it.