Potting Soil Calculator — How Many Bags Do I Need?
Enter your container dimensions and fill depth, choose your bag size, and instantly see how many bags of potting soil to buy — with totals in cubic feet, cubic yards and litres.
Container shape
inches
inches
inches
Bag size
Rounded up to the next whole bag so you never run short
- 1
Volume per container (cu in)
24 × 12 × 10 = 2,880 - 2
Convert to cubic feet
2,880 ÷ 1,728 = 1.6667There are 1,728 cubic inches in one cubic foot (12³). - 3
Bags needed (rounded up)
⌈1.6667 ÷ 2⌉ = 1Always rounded up — buying short mid-project is inconvenient.
How does this calculator work?
Volume (cu ft) = L × W × D ÷ 1728 for rectangular containers, or π × r² × D ÷ 1728 for round pots. Divide total volume by bag size and round up. A 12 × 12 × 10 in pot needs ≈ 0.83 cu ft, so one 2 cu ft bag fills about two such pots. Add an extra bag to allow for 10–20% settling after first watering.
Formula
How this is calculated
Potting soil is sold by volume (cubic feet in the US), so the first step is calculating the space you need to fill. For a rectangular planter or raised bed the volume is Length × Width × Depth; for a round pot or cylinder it is π × radius² × Depth. This calculator works in inches — an easy unit for tape-measure readings — then converts to cubic feet by dividing by 1 728 (= 12³, the number of cubic inches in one cubic foot).
Once the total cubic footage is known, the calculator divides by the bag size you select and rounds up to the nearest whole number, because buying short mid-project is inconvenient. The most widely available bag in the US is 2 cu ft; 1 cu ft bags are common in hardware stores and easier to carry. Multiply the container count by the per-container volume first if you are filling several identical pots.
Soil depth guidelines vary by plant type: herbs and annual flowers typically need 6–8 inches of potting mix; vegetables such as tomatoes, peppers and cucumbers do best with 10–12 inches; shrubs and small trees need at least 18 inches. Potting mix also settles 10–20% after the first deep watering as air pockets collapse, so buying one extra bag for topping-up is a standard gardener's rule of thumb.
Frequently asked questions
Volume = 48 in × 96 in × 12 in = 55,296 cu in ÷ 1,728 = 32 cu ft. At 2 cu ft per bag you need 16 bags. Enter 48 × 96 × 12 in the calculator above to confirm.
Potting mix typically compresses 10–20% after the first thorough watering as air pockets collapse. Top up containers with an extra inch of fresh mix after the initial watering, especially for seeds that need good seed-to-soil contact.
Garden soil is too dense for containers — it compacts tightly around roots, restricts drainage and can introduce pests and disease. Always use a dedicated potting mix for pots and planters; it is formulated to stay loose, drain well and support root growth in a confined space.
Also known as
TG we-Calculate Editorial Team. (2026). Potting Soil Calculator — How Many Bags Do I Need? [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/potting-soil-calculator
TG we-Calculate Editorial Team. "Potting Soil Calculator — How Many Bags Do I Need?." TG we-Calculate. 2026. https://we-calculate.com/calculator/potting-soil-calculator.
TG we-Calculate Editorial Team, "Potting Soil Calculator — How Many Bags Do I Need?," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/potting-soil-calculator
@misc{wecalculate_potting_soil_calculator, title = {Potting Soil Calculator — How Many Bags Do I Need?}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/potting-soil-calculator}}, year = {2026}, note = {TG we-Calculate} }
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