Pot Size Calculator

It depends on the pot's shape, size and how much it tapers. Enter the rim diameter (or length/width for a square pot), height, and base dimension if it tapers, and this calculator gives you the exact volume in quarts, gallons and cubic feet, plus how many bags to buy.

For a straight-sided round pot, volume = pi x radius^2 x height. Most pots taper, though, so this calculator uses the more accurate frustum formula, V = (h/3)(A-top + A-bottom + sqrt(A-top x A-bottom)), which automatically reduces to the plain cylinder formula when a pot's top and bottom are the same width.

About 29.9 quarts per cubic foot, using the exact US liquid-quart definition (NIST Handbook 44). Some brands label bags in dry quarts instead, which are about 16% larger -- this calculator uses the liquid-quart figure, which is the more conservative (smaller) of the two, so it won't undercount the bags you need.

It depends on the pot's height and how much it tapers -- a 12-inch-diameter pot can range from around 6 quarts (shallow, tapered) to over 12 quarts (tall, straight-sided). Enter your pot's exact dimensions above for a precise number rather than a rule-of-thumb estimate.

Yes -- a square or rectangular pot with the same width and height as a round pot holds noticeably more soil, since a square cross-section has more area than a circle inscribed in it (about 27% more, for the same width). This calculator handles both shapes with the same frustum math, just swapping the area formula.

Because most pots do taper, and treating a tapered pot as a straight cylinder overstates its volume, sometimes by 20% or more on a steeply angled pot. Checking the taper box lets you enter the base dimension separately for the accurate frustum volume; leaving it unchecked assumes a straight-sided cylinder or box.

This calculator converts your pot's volume directly into bag counts for the common retail sizes -- 8-quart, 16-quart, 1 cubic foot and 2 cubic foot -- rounded up to the nearest whole bag, since stores don't sell partial bags.

This calculator is built for containers, sized in quarts and gallons the way bagged potting mix is sold. For garden beds, raised beds or bulk topsoil, which are priced and delivered by the cubic yard, use our raised bed soil calculator or soil calculator instead.

A nursery '5-gallon' pot is a trade size, not a literal 5 US gallons -- actual soil capacity is usually somewhat less, often closer to 4-4.5 gallons once you account for the pot's taper and headspace below the rim. Measure your specific pot's dimensions above for an exact figure.

No -- leave an inch or two of headspace below the rim for watering, and expect the soil to settle slightly after its first watering. This calculator computes volume to the rim; round up to the next bag size shown rather than buying the bare minimum.

Calculate one pot's volume above, then multiply by how many identical pots you're filling -- or run the calculator once per pot size if they differ, and add the bag counts together. Buying by cubic feet rather than by bag count is more efficient once you're filling several pots at once.