Stand the bike upright on level ground
Measure seat tube length from the center of the bottom bracket to the top of the seat tube
Measure top tube length from the center of the head tube to the center of the seat tube
Measure effective top tube length horizontally from the head tube center to the seat tube center
Measure head tube length from the top of the head tube to the bottom of the head tube
Measure seat tube angle using the seat tube relative to a horizontal line
Measure head tube angle using the head tube relative to a horizontal line
Measure chainstay length from the center of the bottom bracket to the center of the rear axle
Measure wheelbase from the center of the front axle to the center of the rear axle
Measure standover height from the ground to the top of the top tube at the midpoint
Measure reach from the center of the bottom bracket to the top center of the head tube
Measure stack from the center of the bottom bracket vertically to the top center of the head tube
Compare all measurements with the manufacturer’s size chart
Use a tape measure and a level for accuracy
Measure in millimeters for consistency
Check whether the frame size is listed as seat tube length, effective top tube, or stack and reach
Verify measurements on both sides if the frame shape is asymmetrical