How to use this calculator
- Enter target pressure. Use the line pressure goal for your calipers and tires.
- Enter pedal setup. Set pedal force, pedal ratio and assist multiplier.
- Enter current bore. Use the existing bore for comparison.
- Read required bore. Compare pressure and bore change.
How it works
Master cylinder pressure is force divided by piston area. This page solves the equation backward: bore = sqrt(4 x pedal force x ratio x assist / (pi x pressure)).
Use brake line pressure, brake bias and brake torque for the rest of the brake setup chain.
Worked example
Verified against the live calculator
A 100 lbf pedal force, 6:1 pedal ratio and 1,000 psi target pressure needs about a 0.92 in master cylinder bore before travel and volume checks.
Frequently asked questions
How do you size a brake master cylinder bore?
Multiply pedal force by pedal ratio and assist, then solve bore area from force divided by target line pressure.
Does a smaller master cylinder make more pressure?
Yes. A smaller bore produces more pressure for the same pedal force, but it also requires more pedal travel.
Does this check pedal travel?
No. It checks pressure only. Pedal travel depends on master volume, caliper volume, flex and air in the system.
Can I use this with boosted brakes?
Yes. Enter booster or hydraulic assist as an equivalent assist multiplier when known.
Method & assumptions
- Solves hydraulic pressure only; it does not verify pedal travel or fluid volume.
- Brake system selection also needs caliper piston area, bias, tires, booster curve and stiffness checks.