Free tool
Soil volume helper.
Measure the pot you actually own. Get dry quarts, liters, and a bag count so you don’t come home one bag short.
Mix to buy
What the number assumes
Volume is the inside of the pot, not the decorative outer shell. A one-inch watering lip is left empty by default so mix doesn’t float over the rim. Round pots use the area of a circle. Square and rectangular pots use length times width times the fill depth.
Buy potting mix or container mix, not garden soil. If you are filling several pots, add the bag counts together and keep one extra quart in mind for settling after the first soak.