Stand barefoot with your feet about 6 inches apart
Place a hardback book or ruler between your legs, snug against your crotch
Keep the book level and pull it up firmly to mimic a bike saddle or pant rise
Measure from the top edge of the book straight down to the floor
Use a tape measure for the distance from the book’s top edge to the floor
Have someone else help for better accuracy
Repeat the measurement a few times and use the most consistent result
For pants, compare the inseam length to a pair of pants that already fits well
For cycling, measure in cycling shorts or in the position you plan to ride
Record the measurement in inches or centimeters, depending on what the size chart uses