The coolant weight is listed on a sticker under the hood. On mine, it was near the radiator. (1.5 lbs R134a on mine)
Good info if you are starting with an empty system, not so helpful for a partially filled system. Can sizes vary, so the question of numbers of cans is pointless.
Underfilled is better than overfilled. Stop adding when it starts blowing cold if you lack a gauge.