Potting Soil Calculator

How much potting soil do you actually need?

Buying potting mix by guesswork usually means one too few bags or a half-open sack drying out in the garage. This calculator treats each round pot as a cylinder and works out the real volume, so you know the quarts to buy before you leave for the garden center. Enter the inside diameter and height of your container, how many you're filling, and the size of the bags you plan to buy.

The math it uses

Volume of a round pot is the cylinder formula: V = π × r² × h, where r is half the diameter and h is the height, both in inches. That gives cubic inches, which we convert using 1 dry quart = 67.2 cubic inches (the unit bagged potting soil is sold in) and 1 cubic foot = 1728 cubic inches. Bags needed is the total quarts divided by your bag size, rounded up. These figures are planning estimates, not professional advice — real fill depends on how loosely you pack the mix.

How to use it

1. Enter how many containers you're filling.
2. Measure and type the pot's inside diameter in inches.
3. Type the height (or how deep you'll fill it).
4. Set the bag size in quarts to match what you'll buy.
5. Read the total quarts and number of bags instantly.

FAQ

Should I use the pot's height or a lower fill line?

Enter the depth you'll actually fill. Most gardeners leave about an inch at the top, so subtract that from the height for a tighter estimate.

Why quarts instead of cubic feet?

Bagged potting mix is sold in dry quarts (and sometimes cubic feet). We show both so you can match whatever the label says.

Does this work for square or rectangular planters?

It's built for round pots. For a rectangular box, multiply length × width × height in inches and divide by 67.2 for quarts.

Why round bags up?

You can't buy a partial bag, so we round to the next whole bag. A little extra soil is handy for topping off after it settles.