How to Measure a Hot Tub Cover Radius: A Simple 2-Step Guide

Ordering a new spa cover shouldn't be a guessing game. Knowing how to measure a hot tub cover radius is the most important step for a perfect fit. The most important number you need is the corner radius. If this measurement is off, your cover might be too small to seal the heat in, or so large that it hangs over the sides.

Here are two easy ways to get a perfect measurement using tools you already have at home.

What exactly is a "Radius"?

In simple terms, the radius is the distance from the imaginary square corner of your hot tub to the point where the actual curve begins.

Method 1: Using a Carpenter’s Square 

This is the fastest and most accurate way to measure.

• Step 1: Place a carpenter’s square against the corner of your hot tub.

• Step 2: Look at where the spa's curve starts to pull away from the straight edge of the tool.

• Step 3: The measurement on the ruler from the corner of the tool to that "pull-away" point is your radius.

For more details on sizing, check out this hot tub cover measuring guide. 

Method 2: The Straight Edge & Ruler (No Special Tools Needed)

If you don't have a carpenter’s square, you can use a piece of wood, a ruler, or even a straight piece of cardboard.

• Step 1: Hold your straight edge against the side of the spa so it sticks out past the corner.

• Step 2: Use a second ruler or tape measure to measure from the "Extended Corner" (where the straight edge ends) back to the beginning of the curve.

• Step 3: That distance is your radius.

Important Tips for a Better Fit

• The "Smaller is Safer" Rule: If you are stuck between two numbers, choose the smaller radius. A smaller radius makes the corner of the cover "sharper," which ensures it covers the entire spa.

• The Math: According to our experts, choosing a radius that is 1/2" smaller will actually extend the cover about 1/4" further past the corner. This is much better than having a cover that is too rounded and leaves the corners of your spa exposed!

• Double Check: Measure at least two different corners of your hot tub. Sometimes wear and tear can make one corner look slightly different than the others.

Why Accurate Measurements Save You Money

Measuring your hot tub might feel like a small task, but getting it right is the best way to save money on your energy bills. It all comes down to the Heat Seal.

What is a Heat Seal?

A heat seal is created when your cover fits perfectly tight against the edges of your spa. This "locks" the heat inside. If your measurements are off by even 1 inch, it can create a small gap.

The Cost of a Poor Fit

When there is a gap, steam and heat constantly escape. This forces your heater to work much harder to keep the water warm.

• Higher Bills: A poorly fitted cover can increase your monthly electricity bill by 10% to 15%.

• Chemical Loss: As steam escapes, your water evaporates faster, meaning you have to buy and add chemicals more often.

Need a Replacement?

Once you have your measurement, you are ready to order. If you need a high-quality rounded rectangle hot tub cover replacement, we can help you customize it to your exact specifications.