If you are between sizes, or comparing different brands, look at "Reach" and "Stack" on the bike's geometry chart.
When standing over the bike's top tube with both feet flat, you should have at least 1 inch of clearance on a road bike and 2–3 inches on a mountain bike for safety. 3. Understanding Advanced Fit (Reach & Stack) bike buying guide size
Road bikes are typically sized in centimeters (cm). 4'11" – 5'2": 47 – 50 cm 5'3" – 5'6": 51 – 54 cm 5'7" – 5'9": 54 – 56 cm 5'10" – 6'0": 56 – 58 cm 6'1" – 6'3": 58 – 61 cm If you are between sizes, or comparing different
Mountain and hybrid bikes are typically sized in inches or categorical sizes (S, M, L). 5'0" – 5'4": 14 – 15 inches (Small) 5'5" – 5'8": 16 – 17 inches (Medium) 5'9" – 6'0": 18 – 19 inches (Large) 6'1" – 6'4": 20 – 21 inches (XL) 2. Measure Your Cycling Inseam Understanding Advanced Fit (Reach & Stack) Road bikes
Stand barefoot against a wall with feet 6–8 inches apart. Place a hardcover book between your legs and pull it snugly against your crotch (mimicking a saddle). Measure from the floor to the top of the book's spine.
Your height gives you a direction, but your inseam gives you precision. This is not your pant size; it is the distance from your crotch to the floor.