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Container and Pot Sizes: How Much Soil Do I Need?

vegetables in containersContainer and growing pots come in a variety of sizes. In the United States nursery and garden centers sell pots by the size in inches and gallons. In the United Kingdom, Europe, and most of the rest of the world containers are sold by the size in centimeters and liters.

There are few standards when it comes to container sizes and volumes. To determine the size of a pot measure across the top from one side to the other to determine how many inches or centimeters it is. However, because some pots are long and others are squat and because the sides of some pots are straight and others are tapered, the volume can vary.

How Much Soil Does a Container Need

When it comes to filling a pot with soil estimating how much soil you need is an approximation. Often the volume of a container is measured in liquid quarts or liters, but, of course, when you purchase soil you are purchasing dry (potting soil is not liquid). A dry quart is equal to about 1⅛ liquid quarts. When deciding how much soil to purchase it’s best to factor soil compression that commonly results from moistening and pressing the soil into the pot. Soil compression can add another 15 to 20 percent dry soil to the container. Also take into consideration that when you transplant a plant from one container to another, you will be moving some soil around the roots of the plant.

Take notes on the pots you have and the soil they require. In short order, you will have a realistic estimate of how much soil you will need to purchase when potting plants.

container garden
Container garden on a balcony

Soil for Standard Clay Pots and Plastic Nursery Pots:

This chart will help you translate container sizes for standard clay pots and black nursery pots and give you an approximation of how much soil each will require (again these are dry soil measures):

4 inch pot (10 cm) = 1 pint (0.5L)

5-6 inch pot (13-15 cm) = 1 quart (1L) = 0.03 cu. ft.

7-8 inch pot (18-20 cm) = 1 gallon (4L) = 0.15 cu. ft.

8.5 inch pot (22 cm) = 2 gallon (7.5L) = 0.3 cu. ft.

10 inch pot (25 cm) = 3 gallon (11L) = 0.46 cu. ft.

12 inch pot (30 cm) = 5 gallon (19L) = 0.77 cu. ft.

14 inch pot (36 cm) = 7 gallon (26L) = 1 cu. ft.

16 inch pot (41 cm) = 10 gallon (38L) = 1.5 cu. ft.

18 inch pot (46 cm) = 15 gallon (57L) = 2.3 cu. ft.

24 inch pot (61 cm) = 25 gallon (95L) = 3.8 cu. ft.

30 inch pot (76 cm) = 30 gallon (114L) = 4.6 cu. ft.

See Garden Products Recommended by Harvest to Table

Soil for Hanging Baskets

10 inch (25 cm) = 5.5 dry quarts (6L) = 0.21 cu. ft.

12 inch (30 cm) = 7.9 dry quarts (8.4L) = 0.3 cu. ft.

14 inch (36 cm) = 13.9 dry quarts (15.3L) = 0.5 cu. ft.

Soil for Plant Bowls

8 inch (20 cm) = 1.9 dry quarts (2L) = 0.07 cu. ft.

10 inch (25 cm) = 3.7 dry quarts (4L) = 0.14 cu. ft.

12 inch (30 cm) = 5.5 dry quarts (6L) = 0.21 cu. ft.

14 inch (36 cm) = 8.4 dry quarts (9.2L) = 0.29 cu. ft.

16 inch (41 cm) = 12.0 dry quarts (13.2L) = 0.46 cu. ft.

18 inch (46 cm) = 18.8 dry quarts (20.7L) = 0.73 cu. ft.

21¾ inch (55 cm) = 31.2 dry quarts (34.3L) = 1.21 cu. ft.

Soil for Oval Planters:

12 inch (30 cm) = 3.8 dry quarts (4.1L) =0.14 cu. ft.

16 inch (41 cm) = 7.3 dry quarts (8L) = 0.28 cu. ft.

20 inch (51 cm) = 9.4 dry quarts (10.3L) = 0.36 cu. ft.

Soil for Square Planters:

12 inch (30 cm) = 11.2 dry quarts (12.3L) = 0.48 cu. ft.

15 inch (38 cm) = 23.0 dry quarts (25.3L) = 0.89 cu. ft.

See Garden Products Recommended by Harvest to Table

Soil for Window Boxes:

24 inch (61 cm) = 11.7 dry quarts (12.8L) = 0.45 cu. ft.

30 inch (76 cm) = 15.6 dry quarts (17.1L) = 0.6 cu. ft.

36 inch (91 cm) = 19.7 dry quarts (21.6L) = 0.76 cu. ft.

Soil for Strawberry Pots:

5 gallon = 14 dry quarts (15.4L) = 0.54 cu. ft.

Also of interest: 

Pots and Container Sizes for Growing Vegetables

Soil and Planting Mediums for Containers

Containers for Container Gardens

Dwarf and Miniature Vegetables for Containers

See Garden Products Recommended by Harvest to Table

 

 

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38 Comments

  1. Hi this is Maniraj a research scholar from India I would like to know how to calculate volume of a pot and also what does it mean by 1litre of soil.

    • Volume of a pot… I have a 9 inch diameter pot in front of me as an example… 9 inch top diameter and 7 inch bottom diameter= average diameter of 8 inches.. Formula is.. “Pi” multiplied by “R squared” Radius squared, then multiply that product by the height… So in my case with a nine inch pot I have Pi (3.14159) times (4×4) or 3.14159 X 16= 50.25 square inches multiplied by 8 inches height equals 402 cubic inches. If you want cubic feet then divide the 402 cubic inches by 1,728 cubic inches per cubic foot and you get .237 cubic feet. The 8 1/2 inch container is listed as being .3 cubic feet; the actual measurement would be about .2 cubic feet.

        • Soil density can be measured in a few ways. The presence of sand, silt, loam and organic matter can vary from one soil sample to another–whether you are measuring garden soil or potting soil. Sometimes soil density may include the effect of moisture on the soil. For gardeners, the most common way to measure soil density (garden soil or potting soil) is the hand test: simply grab a handful of soil and squeeze it into a ball. If the soil crumbles apart into many pieces and will not reform when you squeeze it again, then the soil is uncompacted and dry; this soil might be termed light or friable. Soil that breaks apart into a few large chunks that easily reform when you squeeze them is a sign of uncompacted soil with a good amount of moisture. Compacted soils will not break apart in your hand, but are malleable and plastic-like in their consistency when moist; then are hard and unbreakable by hand when dry; this soil would be termed heavy or dense. Other ways to measure soil density include the Protor test; this test requires that three different layers of soil are placed into a cylindrical tube in sequence. A standardized weight is dropped onto the soil repeatedly and the results are measured. The sample then dries overnight and is weighed in order to measure the moisture content. The Nuclear Density Gauge Test is done with a small device that can be transported between testing sights. It operates by measuring the occurrence of a radioactive isotope in the soil in one of two ways. Either by generating small doses of gamma rays that hit the soil surface and then measuring the backscatter–reflection–of the radiation, or by inserting a probe into the soil which transmits the gamma rays directly. Dense, compacted soils absorb more radiation than uncompacted soils. Nuclear density gauges are an expensive, but accurate, timely and effective means of measuring soil compaction.

    • A gram is .0022 pounds. Is your pot a cylinder or cone shaped? What is the composition of your soil mix? How densely will you pack the soil into the pot?
      Fill your pot with soil and firm it in as you wish. Then empty the pot and weigh the soil. Divide the number of pounds by .0022 and you will know the number of grams. Soil is commonly sold by cubic feet not by weight.

    • Four quarts to a gallon times 20 gallons equals 80 quarts. The size of the plant’s root ball (that is a variable) will displace some of the cactus potting soil. You will likely not want to fill the container to the top. You will likely need an amount between 70 and 75 quarts.

      • I have a yucca 3 trunk in one pot. I’m potting on to a 30cm plant pot with cautus and succulent focus soil. How much soil in litres do I need?

        • Place a layer of soil at the bottom of the new container; set the transplants in place; firm soil in around the rootballs; the soil level around the crown of the plants after transplanting should be at the same level as in the previous container. Be sure to gently firm the soil in around the rootballs. The amount of soil needed will vary depending on the size of the rootballs. A pot 30 cm tall and 33cm in diameter will need 15 litres of soil–not accounting for the size of the rootball.

  2. I have a 100 gallon galvanized container. How many cubic feet or cubic yards of potting soil will I need to plant a few tomato plants, carrots, and lettuce?

    • If you are using purchasing the coco coir as a brick– 12 pounds will be more than enough. If the coco coir is loose, you may want to start with about 2 cubic feet; you may need a bit more once the coco coir has been wetted.

  3. I don’t understand how 12in square (and presumably also 12 high) results in approx. 1/2 cubic foot since 12x12x12 inches is the very definition of 1 cubic foot.

    • You will need to measure the container or pot you want to use to determine the exact amount of soil you will need. Typically nursery growers use round and tapered pots (so you will not have a 12x12x12 container) and the soil is not filled to the brim leaving room for the root ball and space for water to collect and seep into the soil. If your container is square and 12x12x12 inches you will need a cubic foot of soil; this will likely be more soil than you need if you are transplanting a plant into the container.

  4. I seldom to never take time to comment on websites but wanted to let you know this page is fantastically useful! I have wondered for decades, since I was a kid, about the relative pot sizes, and the soil they hold, to the commercial bags of soil, frustratingly labeled in both cubic feet and gallons.
    Now that I am moving to containers for some dwarf trees and root crops, I needed to know cubic yards to have delivered for my 20-30 x-lg plastic pots and bags. You have made this easy. Thank-you.
    And the other pages about how many root crop plants can go in each container is also very useful. Again, thank-you.
    The Harvest to Table site information has been bookmarked, and passed on to family.

    • One litre of dry soil has a wet weight of about 1200 g; one litre of wet soil has a wet of about 1500 g. Soil composition can vary and so the weight can vary.

  5. Hi There, I am planning to grow zucchini, pickling cucumbers, eggplants, mini bell peppers in large plastic bins which are 20in wide and 14in deep. Do I need to fill it to the top, or can i fill it to a depth of 10-11 inches. I am using a premium organic potting mix

    • The plants will draw moisture and nutrients from the planting mix; 11 or 12 inches should be enough soil to hold moisture and nutrients for the full season, but you may want to feed the plants with a dilute solution of fish emulsion every 10 to 14 days through the growing season.

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