Bike Size Calculator

Traditionally inseam times a factor by discipline — about 0.665 for road, 0.6 for mountain, 0.635 for hybrid. Modern geometry means stack and reach describe fit better than seat tube length.

Barefoot against a wall, with a book pressed firmly up into the crotch, measuring from the floor to the top of the book. It is not the same as trouser inside leg, which is usually shorter.

For standover clearance, which matters when you may need to dismount abruptly on rough ground. Modern trail geometry has also lengthened reach, so a rider takes a shorter seat tube than they once would.

A long-standing starting point is inseam × 0.883, measured from the bottom bracket along the seat tube. Adjust from there by feel — a slight bend in the knee at the bottom of the stroke.

A professional fitting adjusts saddle position, stem length, bar height and cleat position to your body and flexibility. For anyone riding regularly it is worth more than most component upgrades.

Consider flexibility and intended use — the smaller frame is more manoeuvrable and can be adjusted upward; the larger is more stable and harder to shrink. A test ride settles it far better than a chart.

The vertical and horizontal distance from the bottom bracket to the top of the head tube. They describe fit far better than seat tube length and are comparable between manufacturers.

Rocking hips while pedalling, pointed toes at the bottom of the stroke, and pain behind the knee. Too low shows as pain at the front of the knee.

Reach to the bars and steering feel. A longer stem stretches the rider and slows the steering; a shorter one does the reverse. It is the cheapest meaningful fit adjustment.

Not the size, though it affects ride feel and how much a frame can be adjusted. Carbon frames often have less seatpost adjustment range than metal ones.

Historically shorter top tubes and different contact points. Many manufacturers have moved to unisex frames with size-specific geometry instead, which addresses the same problem more directly.

Clearance between the top tube and the rider straddling the bike. It matters most on mountain bikes where an abrupt dismount is likely, and barely at all on a road bike.