Bike Fit Calculator

This page handles bike fit in the two places arithmetic can honestly reach. One action turns an inseam into a frame size bracket using the traditional inseam rules, with standover clearance and a bar width, and says plainly that a seat tube length means little on a sloping frame. The other two work in stack and reach: given a frame's geometry, the spacers and the stem, you get exactly where the middle of the bar sits relative to the bottom bracket, and with a saddle height the drop and reach from saddle to bar. The third runs that backwards and solves for the stem length and spacer stack that put the bars on a new frame where they sit on the one you already like. It places parts; it does not fit a person.

Calculator Type
Inseam Unit
Applies to the shoulder width below as well, since both are measured with the same tape.

The traditional inseam rules, given as a bracket rather than a single number, with standover clearance and a bar width from shoulder width.

Barefoot, back to a wall, a book pulled up firmly between your legs, floor to the top of the book. Not the inside leg on a pair of trousers.
Across the back, bony point of one shoulder to the other, in whichever unit is picked above. Leave blank to skip the handlebar line.
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Stack, reach, head angle, spacers and stem give the bar position exactly. Add a saddle height and seat angle and you get the saddle-to-bar drop and reach as well.

Vertical from the bottom bracket to the top of the head tube. It is on the geometry chart.
Horizontal from the bottom bracket to the top of the head tube.
From the geometry chart. Road frames run 71 to 74, mountain frames 63 to 68.
Everything between the top of the head tube and the middle of the stem clamp, measured up the steerer. Add half the stem clamp height.
The number printed on the stem, measured from square to the steerer. Negative if it is flipped to point down. A 17 degree stem sits level on a 73 degree head angle.
Bottom bracket centre to the top of the saddle, along the seat tube. Leave blank to get the bar position on its own.
Positive if the saddle is behind the middle of its rails, negative if forward. Worth up to 30 mm either way.
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Give the frame that fits and how it is set up, then the frame you are considering. This works backwards to the stem length and spacer stack that put the bars in the same place.

The bike that already fits.
From the geometry chart. Road frames run 71 to 74, mountain frames 63 to 68.
Everything between the top of the head tube and the middle of the stem clamp, measured up the steerer. Add half the stem clamp height.
The number printed on the stem, measured from square to the steerer. Negative if it is flipped to point down. A 17 degree stem sits level on a 73 degree head angle.
The frame you are considering.
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