Well, there is not really a set amount. What you want to do is to flush out all the old fluid, with new fluid. This will depend on how contimanated the old fluid is. If the old fluid is real bad, it will take more new fluid to displace the old fluid with, because as you flush out the old fluid, it will mix with the new fluid some what. Also there is also the ABS system that holds fluid, and it will need to be cycled to get all the old fluid out of the system. If the fluid is not to bad, then it may just need a bleed to get the air out of the system. Just to put this into perspective, when I did the master cylinder on my 97 Silverado, I bleed the master cylinder before the install. Then I bleed all 4 wheel cylinders, 6 times each, refilling the master cylinder after doing the back brakes first. Then after bleeding the front brakes, I topped off the master cylinder, and started the process over again. So I bleed each wheel cylinder a total of 12 times each. 1 large can of brake fluid was enough to do the whole job. My wife said Her legs were sore for 3 days after we did the bleed. You can also do a pressure bleed and save your spouse all that peddle pumping. After we were done with my Silverado, the fluid was crystal clear, and look the same as what was in the new bottle of fluid.