50ml of brake fluid is enough to perform a bleed on one set of cycle brakes (front and rear).
If the old brake fluid is particularly dirty or discoloured we recommend completely flushing out the old fluid and replacing with new. In which case you may need additional fluid.
Most of our bleed kits are supplied with 100ml bottles of brake fluid. This is enough to bleed a complete set of brakes 2-3 times.