The field notebook / The Potting Bench
Find room for your next green thing.
Measure a container, compare its usable volume and build a small potting list before buying compost.
Your working space
Use inside measurements. Existing root balls displace some compost. This is a geometric estimate, not a balcony load assessment.
Results & observations
Field notes
Measure the inside, not the decorative rim
The geometric model uses the space inside the container. For a straight round pot, volume is π × radius² × height. For a box, multiply width, length and height. Centimetres cubed divided by 1,000 gives litres. The unfilled top space reduces the height used in the calculation.
Tapered pots need two diameters
For a tapered pot, measure the internal top and bottom diameters. The model assumes a circular truncated cone with a straight wall. When you leave a gap at the top, it also adjusts the diameter at the fill line. Curved walls, drainage features and root balls make the real usable volume different.
Build a practical list
Add containers one at a time and compare their totals. This is an estimate of empty internal volume; do not treat it as an exact shopping quantity or a weight calculation. Check plant-specific container guidance and drainage. The RHS container guide is a useful starting point.
RHS: Growing plants in containers
What is saved?
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