This calculator shows how much a stem swap, a stem flip or a spacer move changes your handlebar height and reach, measured at the stem clamp. Enter your head tube angle, your current and new stem, and any spacer change.
Bike Stem and Spacer Calculator
Estimate handlebar height and reach changes from stem length, stem angle, head tube angle and spacer moves.
How to use this tool
- Head tube angle: from your bike’s geometry chart. Most road and hybrid bikes sit between 71 and 74 degrees, and trail bikes between 64 and 67.
- Stem length and angle: both are usually printed on the stem. Enter the angle as positive when the stem points up and negative when it points down. Flipping a -6 degree stem makes it +6.
- Spacer change: the millimeters of spacers you move from above the stem to below it. Use a negative number to lower the stem.
How it calculates
A stem’s angle is measured from a line square to the steerer, and on the bike that line already tilts up by 90 degrees minus the head tube angle. The tool adds that tilt before it works out rise and reach. Spacers move the stem along the steerer, so each 10 mm of spacers raises the bars by about 9.6 mm and moves them about 3 mm closer on a 73 degree head tube.
Example: flipping a 100 mm, -6 degree stem to +6 on a 73 degree head tube raises the bars 20 mm and moves them 6 mm closer.
Before you change anything
Check your fork maker’s maximum spacer stack, leave the roughly 3 mm gap Park Tool calls for between the top of the steerer and the top of the stem or top spacer, and torque the bolts to the figures printed on the stem. Our guide to raising bike handlebars covers each method and its limits.
