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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.

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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.

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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

 

 

Written by Stephen Albert

Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. Harvesttotable.com has more than 10 million visitors each year.

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  1. I have a Golum plant (jade)that is about 30″ round and high in a 16 inch pot.
    It seems to be loosing peddles .
    We wondered about changing soil, larger pot or ?

    • Flower petals drop when a plant is stressed. It could temperatures too hot or often too cold. It could be that the soil is too rich in nitrogen fertilizer. It could be too much or too little water (a moisture meter might help determine that). If when you water, the water runs straight through the pot, the plant could be root-bound. Once you determine the problem, you may or may not want to re-pot. If you do repot, go up to the next largest pot size; keep the root ball intact when you replant and add new, fresh soil around the rootball.

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