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Potting Soil & Planter Volume Calculator

Measure the inside of each container and enter its quantity. The calculator estimates filled capacity, fresh potting mix and optional whole bags.

Measure inside dimensions. Headspace is the distance from the rim to the soil surface.

Group 1 · Inside diameter: Enter a value.

Group 1 · Inside height: Enter a value.

Shopping summary

Use one potting mix for all groups. Calculate different mixes separately.

Optional shopping allowance, from 0% to 30%.

Optional; leave blank for a volume-only estimate.

Complete every group to see a shopping plan.

Rounded estimates depend on measurements, packing and product labels.

Calculations run in this browser. Normal site services may still make requests.

Measure and enter your pots

  1. Measure each container inside, including its full inside height. Enter the vertical gap you want below the rim.
  2. For a tapered round pot, measure the inside diameters at both the rim and bottom. The soil line narrows when you leave headspace.
  3. Group identical pots together. Add a separate group for different dimensions, then optionally enter rootball volume and one shared bag size.

What this calculator includes

  • Calculates rectangular, straight round and tapered round filled volumes.
  • Subtracts the retained rootball and surrounding old mix when repotting is enabled.
  • Combines up to 20 groups before applying an optional shopping allowance.
  • Rounds whole bags only after adding all groups and distinguishes US dry from US liquid quarts.

When to use it

  • Estimate mix for several new planters with different shapes.
  • Subtract a measured estimate of the rootball you keep when moving a plant.
  • Compare a combined shopping target with a chosen bag volume.

Understanding the estimate

A 40 × 20 × 30 cm box with 5 cm below the rim holds 20 L. Three such boxes with a 4 L retained rootball each need 48 L of new mix.

A tapered pot needs the diameter at the soil line. Shortening its height while keeping the rim diameter overstates its filled volume.

A 10% allowance on 60 L gives a 66 L target. With 20 L bags, buy four and expect about 14 L left under these assumptions.

A US dry quart and a US liquid quart have different volumes. Check the unit printed on the bag; nursery trade gallons are different labels.

Privacy and limits

Your measurements are calculated in the browser. Normal site services may still make requests.

This is a volume estimate, not a guarantee of bag coverage or plant fit. Use separate calculations for different potting mixes.

Frequently asked questions

Use inside dimensions, including full inside height. A nominal pot size may not describe its actual capacity.

It is the vertical distance from the rim to the soil surface. It reduces the filled height.

Measure the inside diameter at the rim and at the bottom. The calculator finds the diameter at your chosen soil line.

Include the retained roots and surrounding old mix. This subtraction does not test whether the rootball fits.

One bag size is shared across the list. Combined demand is divided by that bag volume, then rounded to a whole bag.

No. A US dry quart is about 1.101 L, while a US liquid quart is about 0.946 L.

More useful tools are on the way.

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