Free tool / potting-mix estimate

A little arithmetic. A clearer shopping list.

Enter internal measurements for a simple pot shape. Then match the size and complete unit printed on your bag.

Example inputs, not recommended pot sizes or planting depths. For reservoir systems and irregular containers, use the manufacturer’s growing-media requirement instead.

The calculator needs JavaScript. Manual volumes: rectangular = length × width × fill depth; cylinder = π × diameter² × fill depth ÷ 4. Convert cubic centimeters to liters by dividing by 1,000, then divide the total by the bag volume and round up.

01 / Describe the inside

Container shape

Measurement units

Changing units does not convert the numbers. Re-enter your measurements in the chosen unit.

Internal top diameter (in)

Internal bottom diameter (in)

Full internal depth (in)

Empty headspace below rim (in)

02 / How much new mix?

Number of identical pots

Root-ball displacement per pot (L)

Optional extra (%)

Leave displacement at zero if unknown: this estimates empty pots. Extra is your choice, not a required allowance.

03 / Read the bag label

Bag net volume

Bag volume unit

Dry and liquid quarts differ. These are not imperial quarts. If unclear, use the printed liter equivalent or check with the manufacturer.

Estimated new mix / all pots

Enter your measurements

No account or automatic saving. This is approximate volume arithmetic, not a crop recommendation, weight calculation or structural approval.

Why the type of quart matters ↗

Inside the calculation

How tapered pots and headspace work

Fill height = internal depth − headspace. For a tapered pot, the diameter at that height is bottom diameter + (top − bottom) × fill height ÷ full depth. Filled volume = π × fill height × (bottom² + bottom × fill diameter + fill diameter²) ÷ 12. All dimensions must use the same unit.

From a cavity to whole bags

Subtract the estimated root-ball displacement per pot, multiply by identical pot count, then apply your optional extra percentage. Divide by one bag’s volume in liters and round the batch total up to a whole bag. A new bag can supply more than one pot. The leftover is nominal volume, not a guaranteed measured remainder.

Conversions and limitations

1 cubic inch = 0.016387064 L; 1 cubic foot = 28.316846592 L; 1 US dry quart ≈ 1.101221 L; 1 US liquid quart ≈ 0.946353 L. Source: NIST volume tables. Curved walls, inserts, settling and uncertain measurements limit the estimate. A nursery gallon size label is not an exact liquid-volume measurement.