I never really measure the vinegar/water mixture. It does not take very much, like a 1/4 cup per gallon. I use vinegar for sanitizing my tanks also... easier on the hands, great at killing the odour, and not leathal at low doses to fish.
For general cleaning, use 1 tbs per liter of water. Add more if it does not dry quickly.
For sanitizing, use use 1/2 cup per gallon of water.
Works for me anyway.
Note. I never use a vinegar mixture to clean porous materials like rocks or sponges, just to hard to rinse away once obsorbed.