I believe that the coils are measured when they are untensed. There are some great you tube videos that explain this very well.
Measure the number of turns per inch. That measurement will tell you what spring to buy. Also, you can replace your springs with longer springs. However, you can not use a shorter spring to replace an existing spring. In fact replacing with a longer spring reduces the load on the spring and will make it last longer. Some spring companies even rate their springs by how many "cycles" they are expected to last.
When u wined the spring up after u install it I can adjust for having a different size .. it’s really not as big of deal as you’d think. I’d use whatever is the closest you can find. No worries
I was pleasantly surprised to find the bars to set the tension in the box with the springs. I may have missed that in the description.
I would say that you could use them just don't wind them as much. There are you tube videos on this so I'd advise you to watch them before attempting this.
We recommend staying within 1" length of your original spring, so you can use the 0.207" x 2" x 23" springs.
We recommend replacing your springs with the same measurements as your previous springs. It's very rare to go from a pair of springs to a single spring on a 7' x 16' garage door.