Potting Soil Calculator
Work out potting mix for rectangular planters, round pots or tapered pots: soil volume in quarts, liters and cubic feet, and whole bags for any number of containers.
Interactive calculator · Method POTTING-SOIL-1.0 · Last reviewed: 2026-11-04
Calculate your scenario
Rectangular planter = length × width × fill depth.
Your inputs
Default worked example. Edit the inputs to calculate your scenario.
Default worked example
2,880 cu in per planter × (1 + 10%) × 1 = 3,168 cu in = 51.9 L → 6 bags.
How to use the calculator
Pick the planter shape, enter the inside dimensions in inches and how deep the soil will be, add a settling allowance and the number of identical planters, then the bag size and unit.
What the result means
A 24 × 12 in planter filled 10 in deep holds 2,880 cu in; with 10% extra that is about 51.9 L or 47.1 dry quarts, so 6 bags of 8 qt.
Formula and units
Rectangular planter = length × width × fill depth. Straight round pot = π × r² × depth. Tapered pot = π × depth × (R² + R r + r²) ÷ 3, where R and r are the soil-line and bottom radii (half the diameters). Add the settling %, multiply by the number of planters, then convert: liters = cu in × 0.016387064; US dry quarts = cu in ÷ 67.2006; cubic feet = cu in ÷ 1,728. Bags = total ÷ bag size, rounded up.
Worked examples
24 × 12 in planter, 10 in deep, 8 qt bags: Inside length (rectangular): 24 in; Inside width (rectangular): 12 in; Inside diameter at the soil line (round): 12 in; Inside bottom diameter (tapered only): 9 in; Soil fill depth: 10 in; Extra for settling (example 10%): 10 %; Number of identical planters: 1 planters; Bag size (example 8 qt): 8 qt, L or cu ft; Planter shape: rect; Bag size unit: qt.
Example result: Whole bags: 6 × 8 qt; Total soil in quarts: 47.1 dry qt; Total soil in liters: 51.9 L; Total soil in cubic feet: 1.83 cu ft; Soil per planter: 51.9 L.
Four tapered 14 in pots, 50 L bags: Inside length (rectangular): 24 in; Inside width (rectangular): 12 in; Inside diameter at the soil line (round): 14 in; Inside bottom diameter (tapered only): 10 in; Soil fill depth: 12 in; Extra for settling (example 10%): 5 %; Number of identical planters: 4 planters; Bag size (example 8 qt): 50 qt, L or cu ft; Planter shape: taper; Bag size unit: L.
Example result: Whole bags: 2 × 50 L; Total soil in quarts: 85.6 dry qt; Total soil in liters: 94.3 L; Total soil in cubic feet: 3.33 cu ft; Soil per planter: 23.6 L.
Limitations and common mistakes
Use inside dimensions measured to the soil line, not the rim. US soil bags are labeled in dry quarts (1 cu ft ≈ 25.7 dry qt), which are larger than liquid quarts. Mixes compress in the bag and fluff when opened, so the settling allowance is yours to adjust. Quantity only; no plant, drainage-layer or fertilizer advice.
Treating a tapered pot as a straight cylinder at its rim width, which overstates the soil (by about 30% for a 12 in pot tapering to 9 in).
Sources and assumptions
Method POTTING-SOIL-1.0; last formula review 2026-11-04. Sources and their supported claims. Calculation methodology.