Pots and potting mix

Potting Soil Calculator: How Much Mix for a Pot?

Choose a reference nursery-pot size or enter inside dimensions to estimate potting mix instantly, including fill level, pot count, and space occupied by a root ball.

Use it when you need to: Find how much potting soil or potting mix is needed to fill one or more pots, nursery containers, or rectangular planters.

Calculator

Enter the pot's inside dimensions

Load an example product size or enter inside measurements. The result updates as you type.

Example nursery-pot dimensions Loaded 4 × 2.9 × 3.6 in. These are one product line's labeled dimensions, not guaranteed inside fill dimensions, and may overestimate capacity. Measure inside your pot when possible.

Measurement system

Container shape

Inside top diameter

Inside bottom diameter

Usable inside height

Fill level

Existing root-ball volume (optional)

Leave at zero for an empty pot estimate.

Number of identical pots

pots

Optional extra allowance

For the closest estimate, replace reference dimensions with your pot's inside measurements and usable fill depth.

Estimated potting mix

View calculation details

Geometric capacity per pot
Mix per pot
Total before allowance
Converted total

Geometry-based estimate; actual use varies with pot shape and compaction.

Before you calculate

What this estimate can tell you

Wondering how much potting soil you need for a pot or planter? A nominal pot size or top diameter alone does not define its volume. Start with a reference nursery-pot size, then replace it with inside measurements for a closer estimate; the calculator also supports square and rectangular planters.

How the estimate works

Tapered round pots use the frustum formula, straight round pots use the cylinder formula, and rectangular planters use length × width × height. Inch inputs are converted to centimeters; cubic centimeters are converted to liters and then to US gallons for display.

Assumptions and limits

Measure inside diameter and usable inside height rather than the outside of the pot.
Actual use varies with the pot base, drainage structure, root-ball shape, particle size, and compaction.
You choose the extra allowance for possible settling or spillage; it is not a promise that the full amount will be used.

Worked example

Example: a 4-inch tapered nursery pot

Using the editable 4-inch reference dimensions—4 in across the top, 2.9 in across the bottom, and 3.6 in high—the geometric capacity is about 0.15 US gal. Filled to 90% with no root ball entered, it uses about 0.13 US gal before any optional extra allowance.

FAQ

Common questions

Are nursery-pot sizes standardized?

No. A nominal size usually refers to the top diameter, while height, taper, wall thickness, and capacity vary by product. The examples in this calculator load editable dimensions from one product line; measure inside your own pot for a closer estimate.

Why is pot diameter alone not enough?

Diameter describes only the opening. Two pots with the same top diameter can have different heights and different amounts of taper, so their volumes can be quite different.

What should I enter for root-ball volume?

Use a rough estimate of how many liters of space the existing root ball occupies. If you are unsure, enter zero and treat the result as an upper estimate for an empty pot.

Can I convert a bag labeled in pounds or kilograms directly to liters?

Not reliably. Potting materials have different bulk densities, and moisture changes their weight. Use the bag's volume label when it is available.

Calculation references

Botanically Unique: Clear Nursery Pot DimensionsUsed for the editable 3-, 4-, 5-, and 7-inch nursery-pot reference dimensions, rounded to one decimal place; nominal sizes are not universal capacities.
NIST: SI Units — VolumeUsed to verify the relationship among liters, cubic centimeters, and milliliters.
NIST: SI Conversion FactorsUsed to verify inch, centimeter, US gallon, and liter conversion factors.