Because mountain biking originated in the United Sates, mountain bike frame sizes are measured in inches. Most companies increase frame sizes in increments of two inches.
With European origins, road bikes frames are measured in centimeters. While standard men's sizing typically begins at 52cm, some women's lines make a frame size as small as 38cm.
Kids bikes are sized by wheel measurement. They start at a 12-inch wheel and typically move up in size by increments of four inches until they reach a 24-inch wheel. The frame size is determined by the wheel size.
Companies come up with a bike's frame size by measuring either from the center of the bottom bracket to the top of the top tube, or from the center of the bottom bracket to the center of the top tube. Because of the difference in measurement, frame sizes will differ from one brand to another.
Use stand-over height as a starting point for finding the right frame size. When you straddle the top tube, you should have about an inch or two of clearance to safely mount and dismount your bike.
Article Written By Kathrine Cole
Kathrine Cole is a professional outdoor educator. She teaches rock climbing, backpacking, cycling, and bike maintenance classes. She is a graduate of the National Outdoor Leadership School, a Wilderness First Responder, and a Leave No Trace Trainer.