There are several methods to measure the corner radius. The easiest is to take a framing square and place it into the corner of the spa. Read the number where the acrylic touches the framing square. This measurement is the radius.
See figure 1.
When measuring a radius you want to measure slightly smaller. If a cover is made with to big of a radius it will not fit. If the radius is slightly smaller, the cover will insulate just as well, and you will never notice the difference. You can also get the radius by using 2 yard sticks, or a straight edge and a tape measure.
See Figure 2
You can also download our corner radius chart by clicking here. If the file dose not start to download, right click on it and select "save as". You can then print this page hold it up to your spa to tell you what the radius is. Make sure when you print this not to shrink or expand it at all.