What are stack and reach?

Stack is the vertical distance from the bottom bracket centre to the top of the head tube. Reach is the horizontal distance. Together they define the fundamental frame geometry and riding position.

Why compare stack and reach instead of frame size?

Frame size labels (54cm, Medium, etc.) are inconsistent between brands. Stack and reach are universal measurements that directly describe the riding position. Two bikes labelled "56cm" can have very different stack and reach.

How does stem length affect the comparison?

A longer stem extends your reach. When moving between bikes with different reach values, you can often compensate by changing stem length. This calculator works out the equivalent stem for bike B to match your position on bike A.

What about handlebar height?

Stack determines base handlebar height. You can adjust height with stem angle and spacers, but bikes with very different stack values will always feel different. More than 20mm stack difference is noticeable.

How do spacers affect position?

Spacers raise the stem along the headtube axis. On a bike with 73 degree headtube angle, 10mm of spacers adds roughly 9.5mm of stack and 3mm of reach.

BikeCalcs

Stack and Reach Calculator — Compare Bike Geometries

Compare stack and reach between two bikes with equivalent stem calculations.

Bike A Stack

Current bike

Bike A Reach

Current bike

Bike B Stack

New / comparison bike

Bike B Reach

New / comparison bike

Stem Length (Bike A)

Length measurement

Stem Angle (Bike A)

Negative = drop, positive = rise

How We Calculate This

Stack and Reach Comparison

This calculator compares the geometry of two bikes and determines the stem length needed on bike B to match your hand position on bike A.

Effective Position

Effective reach and stack combine the frame geometry with stem length, stem angle, and spacer height. The stem contribution is calculated using trigonometry based on the headtube angle.

Frequently Asked Questions

Related Calculators

Frame Size Calculator

Find the right frame size based on your body measurements.

Saddle Height Calculator

Calculate optimal saddle height from inseam measurement.

Handlebar Reach Calculator

Determine ideal handlebar reach from torso and arm length.

Stem Length Calculator

Calculate the stem length needed for your ideal reach.

Crank Length Calculator

Find optimal crank length based on leg length and riding style.

Last updated: February 2026

All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.