Potting Soil Calculator

Find out how much potting soil to buy for a raised bed, planter, or container. Enter the dimensions and get the volume in cubic feet, cubic yards, and dry quarts, plus how many bags you need.

Quick Facts

Formula
Volume = length × width × depth (all in feet)
1 ft³ = 1,728 in³ = 27 ft³ per cubic yard ≈ 25.7 US dry quarts.

Your Results

Calculated
Bags needed
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Rounded up to whole bags
Total volume
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Cubic feet
In cubic yards
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For bulk orders
In dry quarts
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Common bag unit

Ready

Enter your bed or container dimensions and press Calculate.

How to calculate potting soil volume

Potting soil is bought by volume, so the whole problem comes down to finding the volume of the space you need to fill. For a rectangular raised bed or planter box, that is simply length × width × depth. The only trick is keeping every dimension in the same unit. This calculator asks for inches, converts each dimension to feet by dividing by 12, multiplies them, and multiplies by the number of identical containers:

Volume (ft³) = (Length ÷ 12) × (Width ÷ 12) × (Depth ÷ 12) × Quantity

Depth means how deep you actually want the soil, not the full height of the bed. Most people leave 1–2 inches of clearance at the top so soil and water do not spill over, so use the fill depth rather than the wall height.

Converting to the units on the bag

  • Cubic feet → cubic yards: divide by 27, since a cubic yard is 3 ft × 3 ft × 3 ft = 27 ft³. Bulk soil for large beds is priced by the yard.
  • Cubic feet → dry quarts: multiply by about 25.7. Many bagged mixes (Miracle-Gro, Fox Farm, Espoma) are labeled in dry quarts, so a 25-qt bag is just under 1 ft³.
  • Cubic feet → cubic inches: multiply by 1,728 (12³), useful when checking round pots by hand.

Common bag and container reference points

  • Bagged potting soil is most often sold in 1 ft³, 1.5 ft³, and 2 ft³ bags; in quarts the common sizes are 8, 16, 25, and 50 qt.
  • A standard 4 ft × 2 ft raised bed filled 8 in deep needs about 5.3 ft³ — roughly three 2 ft³ bags.
  • A 4 ft × 4 ft bed filled 10 in deep needs about 13.3 ft³, which is about half a cubic yard.
  • A 12-inch round nursery pot holds roughly 5–6 dry quarts; a whiskey-barrel planter holds about 25 gallons, or close to 3.3 ft³.

Rounding pots and odd shapes

For a cylindrical pot use π × r² × height instead of length × width × height, where r is the inside radius. This calculator handles rectangular volumes directly; for a round pot, enter its diameter as both length and width and the answer will be about 27% too high (a square that contains the circle), so trim your bag count accordingly, or compute the cylinder volume separately.

Frequently Asked Questions

How many cubic feet of potting soil do I need?
Multiply length × width × depth with all three measured in feet. A 4 ft × 2 ft bed filled 6 inches (0.5 ft) deep needs 4 × 2 × 0.5 = 4 cubic feet. If you measure in inches, divide each dimension by 12 before multiplying, or just let the calculator above do the conversion.
How many bags is that?
Divide the total cubic feet by the size printed on the bag, then round up because you cannot buy a partial bag. For 4 ft³ of soil using 2 ft³ bags, that is 4 ÷ 2 = 2 bags. Using 1.5 ft³ bags it is 4 ÷ 1.5 = 2.67, which rounds up to 3 bags.
Should I buy a little extra?
Yes. Fresh potting mix settles and compacts as it absorbs water and as roots grow, dropping 5–20% below its bagged volume over the first season. Adding about 5–10% extra, or one spare bag on larger projects, lets you top beds off without a second trip.
Is potting soil the same as garden soil or topsoil?
No, but the volume math is identical. Potting mix is a light, sterile blend of peat or coir, perlite, and bark meant for containers; garden soil and topsoil are heavier and denser and are meant to amend in-ground beds. You still compute the volume the same way — only the product and price per cubic foot change.

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