How much drainage and soil for a terrarium? Enter the container shape and the depth you want for each layer. Materials are bought separately, so this page gives a bag count per material, not just one total volume. It runs entirely in your browser and saves or sends nothing.
Volume per layer = footprint area × layer depth. Rectangle: length × width × depth. Cylinder: π × radius² × depth. Bowl: about 0.65 × π × radius² × depth — that 0.65 is a stated approximation for a bowl's curved sides, not an exact volume. Volumes are shown in litres (1 litre = 1,000 cubic centimetres) and in quarts (1 litre ≈ 1.057 quarts). Bags per material = ceiling of layer volume ÷ bag size.
With the rectangle defaults above: footprint 30 × 20 cm = 600 square centimetres. Drainage 3 cm = 1.80 L, charcoal 1 cm = 0.60 L, substrate 8 cm = 4.80 L, top dressing 1 cm = 0.60 L. Total stack 13 cm, total volume 7.80 L, leaving 17 cm of headroom in a 30 cm container. At the default bag sizes, that is 1 bag of each material.
Layer shares disagree across sources — drainage is quoted at 15–20% of height by some guides and about 25% for closed builds by others, charcoal at about 0.5–1 cm, substrate at about 25–35% or about 1.5 times drainage — so this page does not hard-code one recipe. Set the depths for your plants and container, and the page will warn you if the stack exceeds about two-thirds of the container height, leaving too little room for plants to grow.
Is the bowl figure exact? No, it is an approximation; measure a real bowl's volume with water if you need an exact figure. Does this choose plants or a closed vs open build? No. This page only calculates volumes; plant choice, watering and ventilation are separate decisions. This page is not gardening or veterinary advice.
This is a free, single-purpose calculator. All calculation happens in your browser. No account, no upload, no tracking by this page beyond any ads Google may serve after approval.