Calculate pot volume for round or rectangular pots from inside diameter, length, width and soil height, with totals in gallons or liters.
- All Math and Numbers Calculators
- All Volume Calculators
- Vessel Volume Calculator
- Cylinder Capacity Calculator
- Drum Capacity Calculator
- Circle Volume Calculator
Pot Volume Formula
Round pots use the frustum formula. Rectangular pots use length × width × depth.
V_round = pi * h * (D_top^2 + D_top*D_bot + D_bot^2) / 12
V_rect = L * W * H
- V = volume of soil the pot holds
- D_top = inside diameter at the top
- D_bot = inside diameter at the bottom (use D_top for straight-sided pots)
- h or H = soil height or depth, not the full pot height
- L, W = inside length and width of a rectangular planter
Measure inside the pot, not outside. Use the soil line you actually plan to fill to, leaving about 1 inch of headspace below the rim. To convert cubic centimeters to liters, divide by 1,000. To convert liters to US gallons, divide by 3.7854.
Reference Tables
Common nursery pot sizes and their approximate soil volumes:
| Trade Size | Top Diameter | Volume (L) | Volume (US gal) |
|---|---|---|---|
| #1 (1 gal) | 6.5 in | ≈ 2.8 | ≈ 0.75 |
| #2 | 8.5 in | ≈ 6.0 | ≈ 1.6 |
| #3 | 10 in | ≈ 9.5 | ≈ 2.5 |
| #5 | 11 in | ≈ 15 | ≈ 4.0 |
| #7 | 14 in | ≈ 22 | ≈ 5.8 |
| #15 | 17 in | ≈ 49 | ≈ 13 |
Common bagged soil sizes and the volume each one fills:
| Bag Size | Liters | US Gallons | Cubic Feet |
|---|---|---|---|
| 8 qt | 7.6 | 2.0 | 0.27 |
| 16 qt | 15.1 | 4.0 | 0.53 |
| 25 qt | 23.7 | 6.25 | 0.84 |
| 1.5 cu ft | 42.5 | 11.2 | 1.5 |
| 2 cu ft | 56.6 | 15.0 | 2.0 |
Example and FAQ
Example. A round pot with a 12 in top diameter, 9 in bottom diameter, and 10 in soil height:
V = π × 10 × (144 + 108 + 81) / 12 = π × 10 × 333 / 12 ≈ 871 cubic inches ≈ 14.3 liters ≈ 3.77 US gallons. One 25 qt bag covers it with a little to spare.
Why does the calculator ask for soil height instead of pot height? You almost never fill a pot to the rim. Subtract about 1 inch from the inside height so the soil line matches what you will actually plant.
Does a "1 gallon" nursery pot really hold 1 gallon? No. Trade gallon sizes are nominal. A #1 pot typically holds about 0.7 US gallons of soil. Use the calculator with your real measurements for accurate planning.
Why does my bag count seem high? Potting mix settles and compresses around root balls. Buy 10 to 15 percent more than the calculated volume if you are filling many pots at once.
How do I handle a square pot that tapers? Use the rectangular mode with the average of the top and bottom dimensions. The error is small for typical taper.
