Measuring rounded corners for replacement hot tub spa covers

Save me Pros!

I have a custom made spa attached to my pool. Consequently I cannot find any seller that would have a template for my spa’s make and model. I am really worried about measuring the rounded corner incorrectly. Give me some tips so I can be confident in my measuring!

Love your site!

Sallie B. – Washington


We will cover this topic in such great detail, and with so many pictures, you will be completely confident in your measurement when you go back to your spa.

Measuring radius of a cornerFirst, most hot tubs have rounded corners. The question is, how rounded? Is it rounded like a soup can, a gallon paint can, or a 50 gallon trash can? The measure of the curvature is called the radius. Normally, a radius is measured as half the distance across a circle, or half the diameter of any circle. When measuring your hot tub, it is more difficult as the corner represents only one quarter of a circle!

Three inch radius corner

Three inch radius corner

Looking at this illustration, the red A line is how a radius is measured when you have a complete circle. The radius is half the distance across the circle (the diameter). For a cover, we will take the measurement shown in this illustration by the blue B dimension, outside the corner of the circle. The key to this illustration is to note that the A and B distances are exactly the same!

Now, lets illustrate how it looks to measure for the B length in the real world. The first picture shows the carpenter’s square on a 3 inch radius corner. The radius measurement should be rounded DOWN when it falls between full inches. The smaller the radius, the less will be cut off the corner of the cover. We will see below what happens when the radius measurement was too large.

5 inch radius corner

5 inch radius corner

This second picture illustrates a five inch radius corner. The radius is more exactly a 5.5 inch radius, but for a cover, it is better to have the cover slightly larger to insure some looseness as covers do tend to shrink over time. A looser fit will also help your cover to close more easily with the skirt less likely to fold up under the cover.

Still looking at this picture, imagine if the cover was made with an eight inch radius. See where the eight inch radius would fall on the carpenter’s square?

Yes, it would not fit! This picture shows a radius corner cover that was cut too large.cover corner radius too large

And finally, another picture showing a very large radius corner cover, on a hot tub corner that was not such a large radius corner.

With this instruction, you will be more confident when you measure. If you do not have a carpenter’s square, as these pictures show, use any straight edge – a 2×4, a newspaper, a yard stick – and lay it along one side. Then use a standard tape measure to measure back from your straight edge to the side of the hot tub.

Happy Tubbing!

Ethel Elliott

Written by HotTubCoverPros

+Ethel writes about all things backyard with a focus on replacement hot tub spa covers. You can also chat with Ethel on Twitter!

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