If the trans is empty and the convertor is empty, usually about 10 quarts.
Best bet is to fill the trans with engine off. Add fluid until it shows about 2" overfull on the stick. Then start the engine and run it through the gears. That should be pretty close. Warm it up and add if necessary.
If you are starting with a "dry" unit, I usually pour in about 6 quarts. Jack the back wheels up. Run it through the gears. Stop the rear wheels with the brakes and put it in Park. Then add as necessary.
