Bike Size Calculator

Selecting the correct bicycle frame size is the foundational metric for optimal power transfer, aerodynamic efficiency, and injury prevention. A mathematically sound bike fit relies heavily on the rider's inseam rather than overall height, as leg length dictates the critical distance between the bottom bracket and the saddle. Riding a heavily mis-sized frame severely alters the rider's center of gravity, leading to anterior knee pain (from a saddle placed too low) or lower back and hamstring strain (from a saddle placed too high).

This calculator utilizes empirical multipliers standard in frame building to establish the theoretical seat tube length. For road geometries, the C-T (Center-to-Top) measurement is typically Inseam × 0.70. The tool also provides the Greg LeMond saddle height benchmark, establishing a baseline measurement from the center of the bottom bracket to the lowest point of the saddle's top curve. Note that crank arm length, pedal stack height, and shoe cleat depth will require minor micro-adjustments to this baseline.

The calculator determines frame size based on proportional multipliers specific to the bicycle's geometry. The formulas calculate the theoretical Center-to-Top (C-T) seat tube length.

Where:
Inseam = Leg length measured from the crotch to the floor barefoot (in cm).
Saddle Height = The LeMond formula measurement from the center of the bottom bracket to the top of the saddle.