It’s important to know the hinge direction on the cover. When you determine the direction you want your cover to fold, take the A-Measurement – the dimension PERPENDICULAR to (across) the hinge. Measure to the outside edge of the top of the spa. When measuring the shell of the hot tub, measure to the outside edge of the acrylic lip so the cover will be big enough and the skirt will hang correctly.
Next, take the B-Measurement – The B-measure will be measured along the direction you want the cover to fold – the dimension HORIZONTAL to the hinge. Measure to the outside edge of the top of the spa. When measuring the shell of the hot tub, measure to the outside edge of the acrylic lip so the cover will be big enough and the skirt will hang correctly.
3. Corner Radius Measure
An easy way to measure a corner radius is to use a carpenter square (pictured below). Place the square against the outside corner of the spa. The point where the corner curve first touches the carpenter square is the corner radius.
If the measurement falls between full inches, round the radius dimension DOWN to the nearest inch. In this picture, the hot tub radius is exactly 9.5″ but a cover made to 8″ or even 7″ radius will give a little leeway on the fit. Making the cover corner a bit larger does not impact the insulating performance (R-value) of the cover.
If you don’t have a carpenter square, download and print this template and hold it over your spa corner to measure the corner radius.