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Bleed Volume Calculator — Hydraulic Brake Fluid
Calculate the correct hydraulic brake fluid volume for bleeding your brakes.
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 × 3 (a generous purge allowance to fully flush old fluid, not the amount the brake actually holds)
- In practice a full front + rear set uses about 50 ml, so a 100 ml bottle covers 2-3 full sets — the per-brake figure here is deliberately conservative so you never run short mid-bleed
- Different brake systems use different fluids — always check before buying, and never mix mineral oil with DOT
Frequently Asked Questions
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.
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.
A 100 ml bottle is usually enough for 2-3 full sets (front + rear) — a single full set typically consumes around 50 ml. This calculator gives a generous per-brake purge allowance (roughly 3x the system volume) so you always have enough on hand; the figure is the amount to buy, not the fluid the brake actually holds.
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.
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.
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Last updated: February 2026
All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.