How much Water For This Plant

I know it’s by volume of the pot. It’s a 3 gallon pot I’m just unsure how to figure that out. The plant is 2 1/2 months old

Water it until you get some runoff. If you are growing organic, then water slightly less next time (water a little less than it takes to get runoff). If you are feeding with salt based nutes then always water until you get runoff.

Water slowly, until you get slight runoff. It's never going to be the same from person to person, plant to plant, or even watering to watering.

In a 3gal pot, if you really take your time, you'll likely be able to run close to a gallon of water to hit the max water absorption point of your medium before you start to get run off