Spa cover corner radius measured the easy way!

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I get a lot of questions when it comes to measuring hot tubs for a new cover. And why not? They’re expensive and you want to make sure everything is correct.

We have excellent Print & Measure Sheets on our Spa Covers Page, but many people get tripped up on measuring the corner radius. Fortunately, you don’t need to be a master of geometry to get it right the first time.

Why can’t you just look up my hot tubs measurements?

If only it were that easy! Spa manufacturers are notoriously secretive about their product specifications because they only want you to buy direct or through their dealers. On a cover, that can add hundreds of extra dollars to the cost.


Should I measure the old cover or the spa?

You’ll get the most accurate results measuring the spa shell instead of the old cover for a couple of reasons. First, covers are manufactured slightly larger than the specified measurements (up to an inch). Second, covers relax and deteriorate over time, making them harder to measure correctly.

Use a carpenters square.

The easiest way to measure a corner radius is with a carpenter square. Simply place the square against the outside rim of the spa in the corner. The point on the inside of the framing square where the corner curve first touches the square is the corner radius. Easy!


Note: If the rim of the spa shell is stepped, measure using the larger of the steps.

Straight edge and ruler method.

No carpenters square? No problem. Grab a straight edge (a broomstick or yardstick works well) and a tape measure or ruler.

Place the straight edge against the rim, extending it past the curve. Now, measure from the straight edge to where the curve straightens out.

You’ll get the same dimension you would with a carpenters square, you’ve just got to hold two things at once. For larger spas, have someone help hold everything square while you measure.


Note:If the rim of the spa shell is stepped, measure using the larger of the steps.

Always round a radius measurement down to the nearest inch or so.

A smaller radius simply extends the cover beyond the corner of the tub. A radius that’s too large and the cover will not extend enough to cover the corner.

That may seem counterintuitive, but think about it this way: a perfectly squared cover will have a 0” radius. That would definitely cover any curved corner, it just might look a little weird.

Bottom line: if you measure a 5 ½” radius (like our photos above), round down to 5” to ensure the cover clears the corner.

Does my cover “need” a corner radius?

The short answer is no, but it’s worth it to take a radius measurement if your tub has curved corners. Say your tub has a 10” corner radius and you go with a zero radius cover. You’re going to have 5” of cover overhanging each corner.

Not only will it look weird, but you’ll be constantly running into it as you walk around the spa, which risks damaging the cover. Additionally, this overhang won’t be supported by the spa shell, risking foam core breakage.

Not convinced? Try taping a square piece of cardboard onto your cover to emulate a zero radius cover.

Do you have a special situation that makes measurement difficult? We’d love to hear from you! Give us a call or shoot us an E-Mail. We’ll make sure you’ve got everything just right.

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