Potting Soil Conversion Calculator: Quarts, Cubic Feet, Gallons, Litres and Bags
Bagged mix is sold in dry quarts, pot sizes are quoted in inches, nursery pots are quoted in "gallons" that are not gallons, and bag labels switch to cubic feet. This converts between all of them and tells you how many bags a given container actually takes.
Four different units for one bag of dirt
A small bag is labelled in dry quarts. A big bag is labelled in cubic feet. Buckets are described in gallons. Everything outside the US is in litres. And the pot you are filling is described in inches - or, if it came from a nursery, in "gallons" that are not gallons either.
None of that is anyone's fault, but it is why the arithmetic goes wrong so often. This converts between all of them and finishes with the two numbers that actually decide the shopping trip: how many containers your soil fills, and how many bags one container takes.
| Example | Cubic feet | Dry quarts | US gallons | Litres | Approximate dry weight | Containers this fills | Bags to fill one container |
|---|---|---|---|---|---|---|---|
| 1 cubic foot of mix, filling 5-gallon buckets | 1.00 cu ft | 25.7 | 7.48 | 28.3 | 20 lb | 1.6 | 1 |
| 25 dry quarts, filling 12-inch pots | 0.97 cu ft | 25.0 | 7.27 | 27.5 | 19 lb | 1.7 | 1 |
| 50 litres, filling a 16-inch pot | 1.77 cu ft | 45.4 | 13.21 | 50.0 | 35 lb | 1.4 | 1 |
| 2 cubic feet, filling nursery "1 gallon" pots | 2.00 cu ft | 51.4 | 14.96 | 56.6 | 40 lb | 20.2 | 1 |
| 8 dry quarts, filling a window box | 0.31 cu ft | 8.0 | 2.33 | 8.8 | 6 lb | 0.5 | 3 |
| Unit | Cubic feet (cu ft) |
|---|---|
| cubicFoot | 1 |
| dryQuart | 0.04 |
| usGallon | 0.13 |
| litre | 0.04 |
These are exact unit definitions, not estimates. ★ The one that catches people: potting soil is sold by the DRY quart (1.101 litres), not the liquid quart (0.946 litres), so a cubic foot is 25.7 dry quarts rather than the 29.9 you get if you use the liquid figure. US gallons here are liquid gallons, which is what a bucket is measured in. Note that none of these are the same as a nursery "gallon" pot - see the container table.
| Container | Usable soil (cu ft) |
|---|---|
| bucket5 | 0.62 |
| pot10 | 0.35 |
| pot12 | 0.57 |
| pot14 | 0.86 |
| pot16 | 1.22 |
| nursery1 | 0.10 |
| nursery3 | 0.34 |
| windowBox | 0.68 |
Round pots are calculated from their nominal top diameter and a typical depth for that diameter, then reduced by roughly an inch of headroom so the soil does not wash over the rim - a full-to-the-brim figure overstates what you need to buy. Real pots taper, so treat these as close estimates rather than exact volumes; if you have the pot in front of you, the site's potting soil calculator works from your own measurements. ★★ The two nursery rows are the important ones: a trade "1 gallon" pot holds about 2.8 litres and a "3 gallon" about 9.5 litres, well short of the 3.79 and 11.36 litres those names imply. Nursery pot sizes are trade designations, not measurements, and this is the single most common reason a soil calculation comes out short.
| Bag | Volume (cu ft) |
|---|---|
| qt8 | 0.31 |
| qt16 | 0.62 |
| qt25 | 0.97 |
| cf1 | 1 |
| cf1_5 | 1.50 |
| cf2 | 2 |
| l50 | 1.77 |
Converted from the labelled size using the exact unit definitions above. Bag labels are the compressed volume at packing; mixes containing peat or coir loosen when moistened and worked, so the same bag often goes slightly further in practice than the label suggests. Buying by cubic feet is usually cheaper per unit volume than buying the same total in small quart bags.
Assumptions and limits
- Dry quarts, not liquid quarts. Bagged growing media is a dry good and is labelled accordingly; using the liquid quart overstates a cubic foot by about 16%.
- Container volumes assume roughly an inch of headroom below the rim and a typical depth for each nominal diameter. Pots taper differently, so these are close estimates.
- Nursery pot "gallons" are trade sizes rather than measurements and hold noticeably less than the name suggests.
- Weight is a rough guide at about 20 lb per cubic foot for a dry peat-based mix. Bark-heavy or sand-amended mixes are heavier, and any mix watered in is far heavier.
- Bag labels describe compressed volume at packing. Loosened and moistened, a bag usually goes a little further.
The dry quart is the one that catches people
There are two quarts in American measure. The liquid quart is 0.946 litres; the dry quart is 1.101 litres, about 16% larger. Growing media is a dry good and is sold in dry quarts.
Use the liquid figure and a cubic foot appears to hold nearly 30 quarts. It holds 25.7. Do that across a whole raised bed or a row of pots and you finish the job several bags short, which is the usual version of this mistake - people rarely buy too much.
A "1 gallon" nursery pot is not a gallon
Trade pot sizes are names, not measurements. A #1 pot - what everyone calls a one-gallon - holds roughly 2.8 litres of soil rather than the 3.79 litres a US gallon actually is. A #3 holds around 9.5 litres, not 11.4.
The gap is roughly a quarter, and it compounds: potting up twenty #1 pots takes about fifteen litres less mix than the name implies, which sounds like good news until you realise every soil estimate you have read that used the nominal figure was overstating how much those pots hold, and understating how many you can fill.
If precision matters, measure the pot and use the site's potting soil calculator on the actual dimensions. The container table here is for the common sizes when you do not have the pot to hand.
What the weight figure is for
Twenty pounds a cubic foot is the dry figure, and it is the one printed on bags. It is not the number that matters for a balcony, a roof, or a shelf bracket.
Watered mix holds a great deal of water: two to three times the dry weight is a fair planning range, and a large planter that weighs 30 lb coming off the shelf can be over 100 lb after a thorough soak. Work out the wet figure before deciding what a railing planter can carry, not the bag weight.