Pot Volume Calculator — Calculate Plant Pot Volume

Measure the internal diameter at the top and bottom, and the internal depth. For round pots, use the frustum formula for an accurate volume.

Cordon tomatoes need at least 20-30 litres of compost per plant. A typical 30cm pot only holds about 12-15 litres, so it is too small for most tomatoes. Use a 40cm+ pot (around 30 litres), a dedicated tomato planter, or a grow bag.

A pot size in cm refers to the rim diameter, not the volume — litres depend on depth and taper. A typical 30cm round pot (about 24cm deep) holds roughly 12 litres; a deeper, less-tapered 30cm pot can reach 15 litres or more. Enter your actual top diameter, bottom diameter and depth above for an exact figure.

Pot size (e.g., 2L, 3L) refers to the volume of compost it holds. Named sizes (e.g., 9cm pot) refer to the diameter.

Leave 2-3cm of space at the top for watering. For very deep pots (40cm+), you can fill the bottom third with broken polystyrene to save on compost.