It is all determined by the weight of your grain, the temperature at which you wish to mash and factors determined by your equipement and ambient temperature.
In general you will want between 1-1.5 quarts of water per pound of grain at about 170F to achieve a mash temp around 150F
Sparge with about 0.5 gal per pound of grain of around 175-180F water
The grain and your system will absorb/loose about 0.1-0.2 quarts of water
As every system and technique varies there are no hard numbers to give you. My advice is use a set of numbers from the above suggestions and have some boiling water and some cold water on hand so you can adjust your mash temp to where you want it.
Measure your volumes and temperatures carefully and write them down. The next time you brew you start "dialing" in your system by adjusting volumes and temperatures to achieve your goal. After several brewing sessions you will start to know what you need to do with your system - eg "1.3 quarts of 176F water to will achieve a mash temp of 153F"
Good luck, have fun and remember if your numbers are off some you still get beer!