To measure for a hot tub cover, measure the spa shell itself from edge to edge in inches, then add 1 inch to both length and width.
Ordering a replacement cover starts with one rule: measure the spa, not the old cover. Old covers warp, shrink, and sag, so they lie about the true dimensions. Grab a tape measure and a carpenter’s square, and you’ll have everything needed in about ten minutes.
Why You Measure the Spa, Not the Old Cover
The old cover is a trap. Foam cores compress, vinyl stretches, and covers sit crooked after years of weather. A warped cover can be an inch or more off from the actual spa shell, so your new cover would inherit that error. Instead, remove the old cover and measure the acrylic shell itself — not the wooden cabinet frame. If there’s a narrow top rail just below the acrylic edge, include it.
The Core Measurements You Need
Every order depends on four numbers: length, width, corner radius, and skirt length. Gather all four before ordering.
- Length and width: Measure the longest and widest sides in inches from the outer edge of the acrylic shell.
- Corner radius: For rounded corners, hold a carpenter’s square against the corner and read the distance from where the curve begins to where it ends.
- Skirt length: Measure from the top of the spa to the bottom of the cabinet, then add about 1 inch for shrinkage. Round up to the nearest whole inch.
- Folding axis: Note which way the cover should fold — usually across the shorter dimension.
Special Shapes: Round, Angled, and Multi-Sided Spas
Not every hot tub is a rectangle. For different footprints, the method changes slightly but stays simple.
- Round spas: Measure the diameter straight across the widest point.
- Angled or cut corners: Measure overall length and width, then the cut corner size and adjoining sides. Note which corners are cut vs. square.
- Six- or eight-sided spas: Measure total length from one side straight across to the opposite side.
- Complex curves: Lay cardboard over the corner, trace the curve, and send the trace with your order. Two rulers at right angles work for simple radius checks.
Safety Straps: Measure Them While You’re At It
Many covers need safety straps for windy weather. These are measured separately from the skirt. Double-check against your skirt measurement before ordering.
Once you have your numbers written down, you’re ready to shop. If you’re also considering a cover for a standard tub, our tested roundup of the best bath tub covers can point you to a solid pick.
| Measurement | How to Measure | Rounding Rule |
|---|---|---|
| Length | Outer edge of acrylic, longest side | Up to nearest 1/2 inch, then add 1/2 inch |
| Width | Outer edge of acrylic, widest side | Up to nearest 1/2 inch, then add 1/2 inch |
| Corner radius | Carpenter’s square, curve start to curve end | Round up to nearest 1/2 inch |
| Skirt length | Top of spa to bottom of cabinet | Round up to nearest whole inch, add 1 inch |
| Safety strap | Straight edge down to clip top | At least 1 inch longer than skirt |
| Round diameter | Straight across the widest point | Round up to nearest 1/2 inch |
| Multi-sided | Opposite side to opposite side | Round up to nearest 1/2 inch |
By the end of this guide, you’ll have every dimension needed for a cover that fits properly — in inches, ready to go. Accuracy is the whole game: a correctly sized cover arrives ready to drop in place, securable with properly fitting straps and a tight seal. Your spa stays warm, clean, and efficient all year.
FAQs
Should I measure the old cover or the hot tub itself?
Measure the hot tub shell itself, never the old cover. Old covers warp, shrink, and compress over time, so they no longer reflect the true dimensions. Measuring the acrylic shell edge to edge gives an accurate baseline, and adding extra room accounts for future seal wear.
What does corner radius mean for a hot tub cover?
Corner radius is the distance from where a rounded corner’s curve begins to where it ends, measured with a carpenter’s square held against the corner. This number tells the manufacturer how tight the curve is, so the cover’s corners match the tub’s shape instead of leaving gaps.
Do I add extra inches to my measurements?
Yes. Add 1 inch total to length and width — half an inch per side — for give and shrinkage. For skirt length, add about 1 inch to the measurement from the top of the spa to the bottom of the cabinet. This keeps the cover from pulling tight as materials settle.
References & Sources
- York Region Hot Tubs & Pools. “How to Measure Your Hot Tub.” Explains measuring the spa shell, adding half-inch allowances, and rounding rules.
- Bud’s Spas. “Hot Tub Cover Order Form with Measuring Guide.” Details corner radius, skirt length, and safety strap measurement steps.
- Pools and Cues. “Guide: Measuring for a Spa Cover.” Covers special shapes including round, angled, hexagonal, and octagonal spas.