Potting Soil Calculator for Pots & Containers

How to use the Potting Soil Calculator for Pots & Containers

1. Select Measurement system.
2. Select Container shape.
3. Enter Inside top diameter (in or cm).
4. Enter Inside bottom diameter (in or cm). For a tapered pot, measure at its inside base.
5. Enter Inside length (in or cm).
6. Enter Inside width (in or cm).
7. Enter Inside total height (in or cm).
8. Enter Space left below rim (in or cm). Subtracts unfilled space at the top. Must be less than total height.
9. Enter Number of identical pots.
10. Enter Extra allowance (%). Optional extra for handling or supplier variation; no allowance is assumed.
11. Enter Volume per bag (selected bag unit). Use the volume printed on the bag, not its weight.
12. Select Bag volume unit.
13. Enter Price per bag (currency) if applicable. Optional. Cost uses whole bags rounded up.
14. Enter Bulk price per cubic yard (currency/yd³) if applicable. Optional. Use the same currency as the bag price. Delivery and tax are excluded.
15. Keep every value in the unit shown beside its field.
16. Select Calculate and review each result and assumption.
17. Verify important decisions with local records, labels, extension guidance, or a qualified adviser.

Formula and method

Measure the inside of the empty container. Filled height is total inside height minus space left below the rim. A tapered pot is modeled as a straight-sided circular frustum, and its diameter at the fill line is interpolated. Only fields relevant to the selected shape are used. Units convert the entered dimensions automatically. The result estimates potting-mix volume, not a mix formulation or the pot manufacturer’s nominal capacity.

Worked example

A cylindrical pot with a 12-inch inside diameter and 12-inch inside height holds about 22.24 L when filled to the rim. Leaving 1 inch below the rim reduces the estimate to 20.39 L. Two such pots need about 40.77 L, or two 25 L bags, before extra allowance.

Measuring pots and choosing potting mix

Measure inside dimensions rather than the outside rim. Choose cylinder for parallel round sides, tapered round pot for straight sloping sides, or rectangular planter. Only the relevant dimensions are shown. This is an empty-container estimate: retained mix and root balls reduce the new mix required. Bag shortcuts are examples, not standard package sizes.

For rectangular garden beds and bulk soil orders, use the topsoil and raised-bed soil calculator. Read our raised-bed planning guide and guide to choosing finished compost for material-selection context.

Understanding the result

Treat the calculated values as a planning estimate. Compare them with your field records, product information, local conditions and operational capacity before acting.

Frequently asked questions