Add each kind of container you are filling, with how many of it, and the calculator gives the potting mix in quarts, cubic feet, gallons and liters, then the number of bags in each common size. Pick a vegetable to fill in the pot size the extension services recommend for it.

Potting soil calculator

 

You need about
0 quarts
Bag sizeBagsA mix sold in that size
8 quart0Espoma Organic Potting Mix, 8 qt
16 quart0Espoma Organic Potting Mix, 16 qt
1.5 cu ft (38.6 qt)0FoxFarm Ocean Forest Potting Soil, 1.5 cu ft
2 cu ft (51.4 qt)0Miracle-Gro Moisture Control Potting Mix, 2 cu ft

Bags are sold by the dry quart (1 cu ft = 25.7 qt). As an Amazon Associate Farmer's Delight earns from qualifying purchases. It costs you nothing extra and does not change what we recommend.

How the numbers work

  • Pots and grow bags by gallons use the US gallon, 231 cubic inches. Fabric bags are sold this way, so a "5 gallon" bag takes about 5 gallons of mix. Nursery pots sold as "#5" or "5 gallon" are trade sizes and usually hold a little less.
  • Round pots are treated as a cylinder: the width across the top and the depth. A pot that tapers holds 15 to 25 percent less, so the answer leaves you a bag in hand rather than short.
  • Window boxes are length by width by depth in inches; raised beds are length and width in feet and depth in inches.
  • Bags are sold by the dry quart, which is larger than a liquid quart: a 1 cubic foot bag holds 25.7 dry quarts, and an "8 qt" bag is about 8.8 liters.
  • Leave 1 inch below the rim so water soaks in instead of running off, which is the headspace extension guides ask for. Add 10% for settling: loose mix from a bag packs down after the first few waterings.

Quick reference: one container, filled

Potting mix to fill one container (1 inch headspace not taken off)

11 rows
ContainerDry quartsCubic feetBags
1 gallon pot3.40.13Half an 8 qt bag
2 gallon pot6.90.27One 8 qt bag
3 gallon pot10.30.40One 16 qt bag
5 gallon pot or grow bag17.20.67One 16 qt bag, just short; or half a 1.5 cu ft bag
7 gallon grow bag24.10.94One 1 cu ft bag
10 gallon grow bag34.41.34One 1.5 cu ft bag
15 gallon grow bag51.62.0One 2 cu ft bag, just short
12 in round pot, 10 in deep16.80.65One 16 qt bag
30 in window box, 8 x 8 in28.61.11One 1 cu ft bag, just short
4 x 4 ft raised bed, 10 in deep34313.3Nine 1.5 cu ft bags
4 x 8 ft raised bed, 12 in deep823321.2 cubic yards: price bulk soil

A cubic yard is 27 cubic feet. Past about 20 cubic feet, a bulk delivery of garden soil and compost usually costs less than bags; potting mix in bags is for pots.

Free to reuse with credit and a link to this page (CC BY 4.0).

What to fill them with

Containers need a soilless potting mix, not garden soil, which packs down and drowns roots in a pot. Which bag suits which crop and climate is in the best potting mix for container vegetables, and the pot each crop needs is in the container size chart.

A raised bed is different: fill it with a blend of topsoil and compost, or a raised bed mix, since a bed full of bagged potting mix costs a lot and dries out quickly. See raised bed gardening for beginners.

Containers in the sizes above

As an Amazon Associate Farmer's Delight earns from qualifying purchases. It costs you nothing extra and does not change what we recommend.

Questions

About 17 dry quarts, or two-thirds of a cubic foot. With an inch of headspace and some settling, one 16 quart bag nearly fills it; buy a 1.5 cubic foot bag to fill two.

About 25.7 dry quarts, which is how bags are labeled. In liquid quarts it is 29.9.

Usually, if last season's plants were healthy: mix it half and half with fresh mix or compost. See the potting mix guide.