Stand the bike on level ground
Measure the seat tube from the center of the bottom bracket to the top of the seat tube
Measure the top tube from the center of the head tube to the center of the seat tube
Measure the effective top tube by using a horizontal line from the head tube to the seat tube
Measure the head tube from top to bottom
Measure the chainstay from the center of the bottom bracket to the center of the rear axle
Measure the wheelbase from the center of the front axle to the center of the rear axle
Measure the standover height from the ground to the top of the top tube
Check the frame size label if present
Use a tape measure and keep it straight for each measurement