How often should I bleed my brakes?

Bleed annually or when the lever feels spongy/inconsistent. DOT fluid absorbs moisture over time and should be replaced every 12 months. Mineral oil is more stable but still benefits from annual bleeds.

Can I mix DOT and mineral oil?

Absolutely not. DOT fluid in mineral oil brakes (or vice versa) will destroy the seals and caliper. Always check your brake system type before purchasing fluid.

How much fluid do I need to buy?

A 100 ml bottle is usually enough for 2-4 full bleeds (both brakes). The flush process uses about 3x the system volume to fully purge old fluid and air bubbles.

Can I bleed brakes without a proper kit?

It is possible with DIY syringes, but a proper bleed kit for your specific brakes makes the job much easier and reduces the risk of introducing air. Kits cost £15-30.

Why are my brakes spongy after a bleed?

Air is still in the system. Re-bleed, making sure to tap the hose and calliper to dislodge trapped bubbles. Ensure the calliper is the lowest point when bleeding Shimano brakes.

BikeCalcs

Bleed Volume Calculator — Hydraulic Brake Fluid

Calculate the correct hydraulic brake fluid volume for bleeding your brakes.

Brake System

Hose Length

How We Calculate This

Bleed Volume Calculation

System volume: 15-25 ml per brake depending on system
Hose length adjustment: Short (-15%), Standard (baseline), Long (+20%)
Total fluid needed = System volume x 3 (to fully flush old fluid)
Different brake systems use different fluids — always check before buying

Frequently Asked Questions

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Last updated: February 2026

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