To measure your sit bones, you can use a sit bone measuring device available at many bike shops. Alternatively, you can do it at home by sitting on a piece of cardboard or aluminum foil on a flat, firm surface. As you sit down, make sure to maintain a 90-degree angle at your hips. The indentations left on the cardboard or foil are your sit bone impressions. Measure the distance between the center of each indentation to find your sit bone width.