Stack and reach calculator

Stack and reach are on the geometry chart of every modern frame, usually in the same table as the head-tube angle. Stack is the vertical distance from the bottom bracket to the top of the head tube; reach is the horizontal distance to the same point. If a chart gives only top-tube length and angles, look the frame up in a geometry database instead of converting by hand.

Stack and reach describe the frame, not your position. They stop at the top of the head tube. Your hands sit wherever your spacers and stem put them, which is why two frames with the same reach can feel 20 mm apart.

This calculator carries the frame numbers up through the cockpit. Spacers move the bar along the tilted steerer, so they add height and take away reach. The stem then adds length × cos and length × sin of its fitted angle. What comes out is the bar centre relative to the bottom bracket, which is the number you can compare between bikes.

• Stack and reach are defined from the bottom bracket to the top of the head tube, as frame makers publish them.
• The cockpit part is trigonometry, exact for the numbers you enter.
• Handlebar shape is not included. A compact bar and a classic bend with the same clamp position still put the hoods in different places.

What are stack and reach?

Stack is the vertical distance from the bottom bracket to the top of the head tube. Reach is the horizontal distance to the same point. Unlike frame size or top-tube length, they do not change with seat angle, so they compare directly between brands.

Can I match my position on a frame with less reach?

Usually yes, within about 20 mm. A longer stem, fewer spacers, or both will get you there. Beyond that the handling changes, because you shift weight over the front wheel.

What is stack-to-reach ratio?

Frame stack divided by frame reach. Around 1.40 is a racing fit and 1.50 or above is an endurance fit. It is a quick way to sort frames, but it does not tell you which one fits you.

How close is close enough?

Within 5 mm in both directions, the difference is smaller than the variation in how you set the bike up. Ten to fifteen millimetres is noticeable. More than 20 mm and you are riding a different position.

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