So you think you're handy, right? You think to measure a hot tub cover you multiply length x width x height, right? That may be the basics to measuring your spa cover, but there are other things to consider, including the different shapes and sizes available.
First you need to consider the amount of foam required and then you measure from the top of the ideal water line. Generally, the amount of foam required can be from 1 pound to 2 pounds in ½ pound increments for 4 inch foam; for 3 inch foam you would require at least 1 ½ pounds of foam. Then take into consideration where to place the fold in the cover for easy removal, whether it's horizontally or vertically.
If you require a skirt for the hot tub cover you will need to measure it too, plus any strapping your tub may require. As a rule, it is always better to get a hot tub cover that is a little larger than too small. Your best bet is to measure your old hot tub cover as a guide. When ordering, make sure you tell the manufacturer if there are handles, spa entertainment systems and other possible items that may be in the way.
Measuring round tubs : a round hot tub is the easiest to measure. All you do is measure the diameter.
Measuring square or rectangular hot tubs with an overhanging spa lip (over the cabinet): measure length vs. width from the end of the overhanging edge. Remember to decide what length of skirt you would like on your cover.
Measuring square or rectangular hot tubs with the cabinet edge sticking out further than the spa : measure past the spa to the edge of the cabinet (that is jutting out) and make sure the skirt will hang down past the cabinet edge.
Measuring spas with four cut corners : basically, you measure the whole width of the tub as if it was square and the whole length of the spa and round up to the nearest ½ inch. Measure the length of the cut corner, but round down to the nearest ½ inch. Generally, a skirt should be about 3 inches, but you can get less or you may not require one at all.
Measuring spas inset in decks : if the lip sticks overtop of the deck, please ensure you measure the length and width of the outer perimeter of the hot tub, not the inside of the tub. It is also a good idea not to get a skirted model and you really should pay the extra money for a “stand on hot tub cover” (especially if you live in an area where it may become snow covered).
Measuring other shaped hot tubs : ensure you take a length and width and draw out the dimensions, including measuring corners, like hexagon-shapes, corner units, etc. and email or fax the drawing to the hot tub cover manufacturer. Keep a copy for yourself in case an error is made when building your hot tub cover so you have recourse.