Bicycle Fit Calculator

That multiplier is the LeMond method, a formula derived from average leg proportions that positions your knee at close to full extension (but not locked out) at the bottom of the pedal stroke when saddle height is measured from bottom bracket center to saddle top along the seat tube. It's a widely used starting point precisely because it's been validated across a large range of average body proportions, though individual flexibility and pedaling style can still shift the ideal height slightly.

Riding style adds a forward or backward shift to setback (race position adds the least, comfort/endurance adds the most, moving the saddle further behind the bottom bracket) and separately adjusts the saddle-to-bar drop, where race position adds more drop and comfort position subtracts from it. These reflect how aggressive riders push their hips forward over the bottom bracket for power while comfort riders sit further back and more upright.

It's the opposite direction from what you might expect at first glance, but it's intentional: limited flexibility adds to the drop calculation (+1.5 cm) while very flexible riders get -2 cm, because someone with limited flexibility riding in a lower, more stretched position would strain their back and hamstrings, so the formula compensates by keeping the bars relatively higher. Flexible riders can tolerate — and often prefer — a lower bar position without that same strain.

The calculator computes a raw value from inseam × 2.16 mm and then rounds it to the nearest 2.5 mm increment, since that's how most manufacturers size their crank arms (commonly 165, 167.5, 170, 172.5, 175 mm, and so on). You won't find a crank at an arbitrary length like 171.3 mm, so the rounding step reflects what's actually available to buy.