Stem Length Calculator — Adjust Your Reach
Calculate the stem length needed to achieve your ideal reach.
How We Calculate This
Stem Length Adjustment
New Stem = Current Stem + (Target Reach − Current Reach)
Stem length maps roughly 1:1 to horizontal reach, so a 10 mm longer stem adds about 10 mm of reach. This calculator keeps the same stem angle.
Stem angle mostly changes bar HEIGHT, not reach. Horizontal reach = stem length × cos(angle) and bar rise = stem length × sin(angle). Going from a 0° to a 6° stem of the same length changes horizontal reach by only about 0.5 mm but bar height by about 10 mm (on a 100 mm stem). A +6° and a −6° stem give identical horizontal reach.
Headset spacers stack along the steerer, which is tilted at the head-tube angle. A spacer stack of height h raises the bar by h × sin(HTA) and pulls it back by h × cos(HTA) — about 6 mm of lost reach per 20 mm of spacers at a 73° head angle.
Frequently Asked Questions
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Last updated: 2025-02-20
All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.