We go by what waist size we think they will fit. So if we think they will fit someone with a 26 waist, they will be marked as a size 26 in the title. If you'd like to know more, here are some specifics: More often than not, high waisted clothing sits lower than your actual waist line. Because of this, the waist measurement on a pair that will actually fit you will likely be .5-4 inches (1.27- 10.16 cm) bigger than your body's waist (I find that 2 inches / 5.08 cm is the most common difference).