Four explicit models
Rectangular: length × width × filled depth.
Cylinder: π × (inside diameter ÷ 2)² × filled depth.
Tapered round: π × filled depth × (top diameter² + top diameter × bottom diameter + bottom diameter²) ÷ 12. This assumes circular cross-sections with straight tapering sides.
Known capacity: entered usable volume × the unit conversion. This bypasses shape estimation, but the volume you enter must actually describe the usable space.
Units stay explicit
The calculator uses 1 inch = 2.54 cm, 1 liter = 1,000 cm³, 1 cubic foot = 28.316846592 liters, and 1 US liquid gallon = 3.785411784 liters. The last two follow from the length and US gallon definitions. It does not interpret dry measures or nursery trade labels.
NIST length definition · NIST volume definitions · NIST US gallon definition
Rounding does not add a buffer
Each unrounded estimate is multiplied by its container count and added to the plan. Liters and cubic feet are then rounded for display. Whole-bag counts use the unrounded total divided by your entered bag volume, rounded up. Only floating-point machine noise at an exact boundary is absorbed.
Where the estimate stops
Rounded or irregular walls, a false bottom, plant root balls, material already present and settling can change how much new mix is actually used. No extra percentage is added automatically. The estimate does not decide whether a crop will grow well or whether a surface can support the container.
This tool supports up to 20 groups of up to 100 containers each. Keep measurements in the requested units and use decimals rather than fractions.
Back to your estimate