Potting Soil Calculator

Potting mix is sold by volume, so the question is really how much space is inside the container. Measure a round pot, a rectangular planter or a window box, say how far below the rim you want the soil to stop, and the tool returns the volume in litres, cubic feet and US dry quarts, plus how many bags of your chosen size that comes to and how much is left in the last one. A tapered pot is treated as a frustum rather than a cylinder, which matters once the sides slope. Fresh mix settles after the first watering, so a figure with ten percent spare is shown alongside.

Calculator Type
Measured In
The container size and the soil depth come back in this unit too.

Measure across the top on the inside. If the pot tapers, give the base diameter too and the taper is taken into account.

1 to 120 in, which is 2.54 to 304.8 cm.
Leave blank for a straight-sided pot.
1 to 120 in, which is 2.54 to 304.8 cm.
Same unit as the other measurements. Most people leave about 1 in (2.5 cm) so watering does not wash the mix over the edge.
US dry quart and cubic foot bags and metric litre bags are both listed, with the litre equivalent beside each, so you can pick whatever is actually on the shelf.
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Measured In
The container size and the soil depth come back in this unit too.

Inside measurements of a square or rectangular container, trough or raised planter.

1 to 240 in, which is 2.54 to 609.6 cm.
1 to 240 in, which is 2.54 to 609.6 cm.
1 to 120 in, which is 2.54 to 304.8 cm.
Same unit as the other measurements. Most people leave about 1 in (2.5 cm) so watering does not wash the mix over the edge.
US dry quart and cubic foot bags and metric litre bags are both listed, with the litre equivalent beside each, so you can pick whatever is actually on the shelf.
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Measured In
The container size and the soil depth come back in this unit too.

Window boxes are sold by nominal length. Pick the length, then give the inside width and depth, which are usually a little under the outside figures on the label.

The inch sizes are the North American shelf, the centimetre sizes everyone else's. Pick the box you can actually buy -- these are two product lines, not one length spelt twice.
Most boxes run 6 to 10 inches, or 15 to 25 cm, front to back. A blank box uses 8 in, or 20 cm.
Six inches, about 15 cm, of mix is about the shallowest that will hold moisture through a summer day. A blank box uses 7 in, or 18 cm.
A blank box uses 1 in, or 2.5 cm. Enter 0 to fill it to the rim.
US dry quart and cubic foot bags and metric litre bags are both listed, with the litre equivalent beside each, so you can pick whatever is actually on the shelf.
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