GardenCalcs.uk
Drainage Layer Calculator — Pot Drainage Material
Work out crocks or gravel needed for container drainage layers.
Internal diameter across the pot base — the drainage layer fills the bottom, not the rim
Keep it thin: 2-3 cm is plenty. Deeper layers waste root space and can hold a perched water table
Crocks and gravel are cheap and heavy; perlite and LECA are far lighter for big or wall-mounted pots
How many pots of this size you are filling — totals scale across all of them
Weight of gravel per litre (default 1.5 kg/L)
Weight of broken crocks per litre (default 0.8 kg/L)
Weight of perlite per litre (default 0.1 kg/L)
Weight of LECA clay pebbles per litre (default 0.4 kg/L)
How We Calculate This
Volume per pot = π × (Diameter/2)² × Layer Depth (in cm), converted to litres.
Total = Volume per pot × Number of pots. Weight uses material density: gravel 1.5 kg/L, crocks 0.8, perlite 0.1, LECA 0.4.
Frequently Asked Questions
Opinions are divided. Modern thinking says drainage layers can create a perched water table. The most important thing is having drainage holes. A thin layer of crocks stops compost washing out.
Keep it thin — 2-3 cm for most pots. Deeper drainage layers waste root space and can actually hold water.
Broken crocks, clean gravel, perlite, or LECA (clay pebbles). Avoid polystyrene as it can float and break up.
Lightweight Expanded Clay Aggregate. Clay balls that are lightweight and retain some moisture. Good for large pots where weight is a concern.
Yes, drainage holes are essential. Without them, water collects at the bottom and roots rot. If using decorative pots without holes, use an inner pot with drainage.
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Last updated: February 2026
All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.