How to calculate planter and pot volume

What you need to know

Estimate potting mix for rectangular, round and tapered containers. Use consistent units, apply the appropriate method and check the final conversion.

A reliable process

1. Identify the shape or measurement method.
2. Measure carefully using one unit throughout.
3. Calculate volume and convert to liters.
4. Allow for walls, curves and internal equipment when estimating usable capacity.

Worked example

A 50 × 30 × 20 cm box occupies 30,000 cm³, which equals 30 liters of geometric volume.

Common mistakes

• Mixing centimeters and meters.
• Using outside dimensions for inside capacity.
• Rounding too early.
• Skipping a second measurement.