You need to measure your sit bones for an accurate reading…. like this:
There are two boney protrusions in you backside, one to the left and one to the right. They are called your Ischial Tuberosities, but most people call them your “sit bones”. They support nearly all of your weight when you are sitting. They are located to the left and right of your anus. They are usually farther apart on a female than on a male to accomodate the birth canal. You should be able to feel them if you sit on a hard surface and rock slightly to the right and the left. You will feel the increased pressure on them as you rock in that direction.
The easiest way to measure them is with a tailor’s tape measure. Bend over and place the tape on one of the areas where you felt the pressure and pull the tape taunt to the other area that you felt the pressure. Place your finger over the spot on the tape to mark it where it passes over the area where you felt the increased pressure. Then just read the tape where you have it marked with your finger.
If you have a chunk of memory foam like what some of the newer bed matresses are made of, sit on it and before it springs back, measure between the two deepest indentations. Or if you have some thick corrugated cardboard, you can substitute it for the memory foam, but it does not work as well.