How many quarts of soil in a 5 gallon bucket?
By Muzamil Ali · Last updated
A 5 gallon bucket takes about 17 dry quarts of potting soil, not 20. Why bagged mix is sold in dry quarts, and the volume of every common pot size.
A 5 gallon bucket holds about 17 US dry quarts of potting soil, not 20. Five US gallons is 0.67 cubic feet, and one cubic foot is 25.71 dry quarts. The 20-quart figure comes from counting liquid quarts — and bagged potting mix is sold in dry quarts, which are about 16% larger. Be sure you are buying mix rather than garden soil while you are at it, because the difference between them decides whether a container drains at all.
Where the 20-quart answer comes from
Four liquid quarts make a gallon, so five gallons is twenty liquid quarts. That arithmetic is correct and the answer is still wrong, because it is the wrong quart.
- One US dry quart is exactly 67.200625 cubic inches.
- One US liquid quart is 57.75 cubic inches.
- The dry quart is about 16% larger.
A bucket described as "5 gallon" is measured in liquid gallons. A bag of mix is labelled in dry quarts. Convert through volume rather than through the word "quart":
5 US gallons = 5 x 231 cu in = 1,155 cu in
1,155 / 1,728 = 0.668 cubic feet
0.668 x 25.714 = 17.2 US dry quarts
0.668 x 28.317 = 18.9 litres
The soil volume converter does this arithmetic for any bag size and any unit.
So a 25-quart bag fills a 5 gallon bucket with room to spare, and three bags fill four buckets.
The figure 29.92 quarts per cubic foot appears on a great many websites. That is the liquid conversion. Use it and you will believe a container holds about 16% more than it does, buy 16% too few bags and make a second trip.
Everywhere outside the US the unit is litres, and one cubic foot is 28.32 litres. No ambiguity.
How much potting soil for a 12 inch pot?
About 17 dry quarts filled ten inches deep — coincidentally close to the bucket. Page-one results for this question currently offer 8, 12 and 20 quarts, and the spread comes from different assumptions about fill depth and pot shape rather than from anyone being careless.
Here are the figures with the assumptions stated:
| Container | Soil depth | Dry quarts | Litres | Cubic feet |
|---|---|---|---|---|
| 6 in round pot | 5 in | 2.1 | 2.3 | 0.08 |
| 8 in round pot | 7 in | 5.2 | 5.8 | 0.20 |
| 10 in round pot | 9 in | 10.5 | 11.6 | 0.41 |
| 12 in round pot | 10 in | 16.8 | 18.5 | 0.65 |
| 14 in round pot | 12 in | 27.5 | 30.3 | 1.07 |
| 5 gallon bucket | to the brim | 17.2 | 18.9 | 0.67 |
| 16 in square planter | 14 in | 53.3 | 58.7 | 2.07 |
| 24 in window box, 7 in wide | 6 in | 15.0 | 16.5 | 0.58 |
| 36 in grow bag, 14 in wide | 9 in | 67.5 | 74.3 | 2.63 |
| Half barrel, 26 in across | 16 in | 126 | 139 | 4.91 |
| Nursery #1 trade gallon | 6.5 in | 3.2 | 3.5 | 0.13 |
| Nursery #5 trade gallon | 11 in | 15.6 | 17.1 | 0.60 |
Two things to notice. The half barrel needs five 25-quart bags, which surprises people at the checkout. And nursery trade sizes are not liquid gallons at all — a "one gallon" pot holds about 0.93 US gallons, and a "five gallon" nursery pot about 4.5.
The container soil calculator will do any size, including several containers at once and a bag count.
The arithmetic, if you want to do it yourself
A round pot or half barrel is a cylinder:
cubic inches = pi x (diameter / 2)^2 x depth
A square or rectangular planter is a box:
cubic inches = length x width x depth
Then convert:
cubic feet = cubic inches / 1728
US dry quarts = cubic feet x 25.714
litres = cubic feet x 28.317
US gallons = cubic feet x 7.4805
Measure the diameter across the top of the soil, and use the soil depth rather than the full height of the pot — leave an inch of freeboard so watering does not wash mix over the rim.
Worked example
A twelve-inch round pot, filled ten inches deep:
- Radius 6 in, so volume = π × 36 × 10 = 1,131 cubic inches
- 1,131 ÷ 1,728 = 0.654 cubic feet
- 0.654 × 25.714 = 16.8 US dry quarts
- 0.654 × 28.317 = 18.5 litres
One 25-quart bag fills that pot with a little left over. Four of them need three bags.
Why your pot may need less than the table says
Pots taper. The cylinder arithmetic treats a pot as straight-sided. A typical tapered pot holds ten to twenty per cent less than its top diameter suggests. That margin is useful anyway, because mix settles.
Mix settles. Expect to lose another ten to fifteen per cent in the first few waterings as air pockets close. Fill to an inch below the rim, water thoroughly, then top up.
Buy by volume, not weight. Bag weights vary enormously with how wet the mix is. The quart or litre figure is the one that tells you whether it will fill your pots.
One big container beats two small ones
The larger the volume, the slower it dries out, and drying out is what kills most container plants. If you are choosing between sizes, take the bigger one.
Which crops are worth a bucket at all is a separate question — can you grow vegetables in 5 gallon buckets covers it. Salad leaves, bush beans, peppers and a determinate tomato all suit the size; sweet corn, pumpkins and main-crop carrots do not. The tomato guide has the spacing and feeding for the crop most often grown this way.
For raised beds, switch units
Beds are big enough that quarts stop being useful. Bagged soil and compost for beds are sold by the cubic foot, and bulk by the cubic yard — 27 cubic feet.
A 4 × 8 ft bed 12 inches deep takes 32 cubic feet, which is 22 bags at 1.5 cubic feet, or about 1.2 cubic yards loose. The raised bed soil calculator handles that end, and what to fill raised garden beds with covers the mix — unlike a container, a bed wants mineral soil in it rather than potting compost alone, which slumps as its organic matter breaks down.