Got some containers to fill? Here’s a handy soil calculator for pots and raised beds that measures the soil volume you need. Take the guesswork out so you can start gardening!
I’m not a fan of doing math. Jesse is always rechecking my calculations, so I like having tools that give her a break and let me skip the user error stuff. For example: a calculator that tells you how much soil is needed to fill a pot or raised bed.
This potting soil calculator uses container dimensions to tell you how much soil is required in cubic feet— the typical measurement for soil bags. (You can also get this result in liters!) Besides the calculator, you’ll also find out how many bags of soil you need for different planters.
Enjoy!
Garden Soil Calculator
Use this interactive calculator to get the amount of soil you need for your rectangular or circular containers and raised beds. Just enter the dimensions (imperial or metric) to get your results in cubic feet or liters.
Note On Soil Calculator For Pots
This calculator is for containers with straight edges rather than tapered shapes like flower pots. (That’s a whole other math formula.) You may overestimate your soil needs a little bit, but it’s always better to have more than enough!
How Do I Calculate How Much Soil I Need?
Here are the formulas for calculating the soil needed for pots and raised beds in cubic feet. (In case you’re curious.) The formula depends on the shape of your container.
(Note: The potting soil calculator does these calculations automatically.)
Calculate Potting Soil For Round Container
(π * R2 * depth) / 1728 = Volume
*Radius (R) and depth are in inches. Dividing by 1728 converts cubic inches to cubic feet.
Calculate Soil Needed For Raised Bed
length * width * (depth / 12) = Volume
*Length and width are in feet, and depth is in inches. Dividing the depth by 12 converts to feet.
Calculate Soil For Rectangular Planter
(length * width * depth) / 1728 = Volume
*Length, width and depth are in inches. Dividing by 1728 converts cubic inches to cubic feet.
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How Many Bags Of Soil Do I Need?
A large bag of soil is typically around 1.5 cubic feet. Going by that size, here’s how many soil bags you’ll need for various planters and raised beds.
How Much Potting Soil Fills A 5-Gallon Bucket?
A 5-gallon bucket uses about 0.7 cubic feet of soil. You’ll need one bag of soil (1.5 cu ft) to fill about two buckets.
How Much Soil Do You Need For A Grow Bag?
Grow bags (fabric pots) vary in size and dimensions. Here are some typical grow bag sizes, along with the cubic feet of soil and number of soil bags it takes to fill each container.
(Note: This chart is based on Vivosun grow bag dimensions. If your grow bag is a different brand, use these numbers as a general idea of what you’ll need.)
| Grow Bag Size | Cubic Feet of Soil | # of Bags (1.5 cu ft) |
|---|---|---|
| 1-Gallon | 0.15 | 1 bag fills 10 pots |
| 2-Gallon | 0.27 | 1 bag fills 5.5 pots |
| 3-Gallon | 0.41 | 1 bag fills 3.7 pots |
| 5-Gallon | 0.70 | 1 bag fills 2.1 pots |
| 7-Gallon | 0.92 | 1 bag fills 1.6 pots |
| 10-Gallon | 1.37 | 1 bag |
| 15-Gallon | 2.14 | 2 bags fill 1.4 pots |
| 20-Gallon | 2.86 | 2 bags fill 1 pot |
| 25-Gallon | 3.43 | 3 bags fill 1.3 pots |
| 30-Gallon | 4.09 | 3 bags fill 1 pot |
Resource: Cubic Feet to Liters Conversion
How Many Bags Of Soil Do You Need For A 4 x 4 Raised Bed?
A 4×4 raised garden bed that is 10 inches high uses 13.33 cubic feet of soil or nine bags. This amount is based on 1.5 cu ft a bag.
How Many Bags Of Soil Do You Need For A 4 x 8 Raised Bed?
A 4×8 garden bed that is 10 inches high uses 26.67 cubic feet of soil or 18 bags. This is based on 1.5 cu ft per bag.
Notes:
- The cubic feet and bag counts assume that soil is the only thing filling the containers and not anything else like compost. You won’t need as much soil if adding amendments.
- Ten inches is the minimum recommended height for raised beds. Most garden crops need to grow at this depth.
Sources:
- “How Much Compost, Soil or Mulch?,” Texas A&M Agrilife Extension
- “Raised Garden Bed Dimensions,” University of Georgia Extension
- “Conversion Calculator,” Metric Conversions
Best Soil For Container Gardening
When filling containers, choose soil labeled “potting soil” or “potting mix.” These mixes support the air, nutrients and moisture retention needed for potted plants.
» Related: The Best Organic Potting Soil Mix for Hot Peppers In Pots
You can also find bags of soil formulated for raised beds, but that’s expensive! An alternative is to mix even amounts of coarse vermiculite, peat moss and blended compost (Mel’s Mix). You can also do what Epic Gardening recommends by filling the bottom of your taller garden beds with organic materials like dry wood, and then fill the rest with Mel’s Mix.
Source:
- (Bartholomew, Mel, All New Square Foot Gardening, Cool Springs Press, 2018, p. 125)
Container Garden FAQs
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