"full can every other day"

Little and often would be better.

I water my Toms 3 times a day on a hot day, twice (and less water at each occasion) on a cool / overcast day.

My 10L watering can does about 10 plants at a "main watering", and probably 15 plants at an "overcast" watering. So on a sunny day that would be 3L / plant / day. My Toms are in 11" pots.

Mind you, you can't just "measure" the water out, you need to gauge based on experience, but hopefully it will give you a bit of a benchmark