When measuring for a new hot tub cover, there is one important thing to remember
IT HAS TO BE BIG ENOUGH TO FIT!
A bit too big is much better than too small
Make sure the measurements are big enough. It is okay for the cover to be a bit big. It still does it's job. However, a cover that is too small will never insulate properly.
Don't forget that, even though your hot tub might look square, it might not actually be square, so always measure both the length and width to confirm that they are either the same or different. Always err on the side of adding surface area to the cover and don't skimp on the measurements.
You can specify if the hinge is at the centre of the longest side or the shortest side when you order
Hot tub covers can fit in one of two ways. The most popular is a cover that fits only over the acrylic shell (in most hot tubs, the acrylic shell comes out further than the wood or plastic skirt) and in this case, you should measure either the dimensions of your current cover, or, if that is missing or doesn't fit well, from the outside edge of the hot tub shell.
However, if your hot tub resembles the diagram below, with a wood or plastic sill on the outside of the acrylic shell, and you would like your new hot tub cover to cover both the shell and the sill then, obviously, you must measure from the outside of the sill. The cover will perform equally well either way, as long as it is big enough to fit completely over the hot tub shell, but if it covers a wooden sill from the elements then the wood will survive much longer.
X - You should specify your skirt length to be a bit more than this.
Y - Outside dimension of the acrylic shell. This is the normal measurement to specify unless you have a sill and prefer your cover to fully enclose it, in which case specify measurement Z.
Z - Outside dimension of the hot tub cabinet.
Above is an illustration of the best way to measure the corner radius.
Measure the distance from the imaginary corner, A, to the point at which the curvature stops, B.
Round down any dimensions of cut corners or radius corners. If the radius is too big (ie there is too much curvature) or if the cut corner is too long, the cover will never fit the corner properly. But if the curvature is a bit too small (or the cut is too short) that is absolutely fine; there will just be a slight overhang at the corners which actually makes the cover easier to get on and off.
If your cover corners aren't perfectly rounded or cut at 45 degrees then that is not a problem, but you will need to send us a template work with.
Your hot tub cover can look way past its best very quickly if it is not maintained and cleaned regularly!
Chemical in the water vapour that comes into contact with the cover eventually causes the plastic wrapping around the inserts to become brittle and crack. Once that happens the foam inserts will quickly absorb moisture, become heavy and stop insulating properly. Poor water chemistry can also cause bleaching, puffiness within the vinyl and disintegration of the stitching.