Raised Bed Material Calculator — Build Your Own Raised Beds

Timber sleepers are the most popular choice: durable, attractive, and easy to work with. Scaffold boards are a budget option. Brick and stone are permanent but more expensive. Avoid pressure-treated timber if growing edibles — use untreated larch, oak, or cedar.

For vegetables, 200-300mm (8-12 inches) is sufficient for most crops. For root vegetables like carrots, 400mm+ is better. For wheelchair-accessible beds, 600-700mm is recommended. Higher beds need more soil but offer better drainage and less bending.

Landscape fabric on the base prevents weeds growing up into the bed and stops soil mixing with the ground below. On the sides, it helps prevent soil washing out between boards. It is recommended for timber beds but not essential for brick or stone.

The calculator fills the internal cavity — the soil space inside the walls, not the external footprint. A 2.4m x 1.2m bed with 100mm sleepers has a 2.2m x 1.0m cavity, so at 300mm deep it needs about 0.66 cubic metres (the bare external box would suggest 0.86, which over-orders by ~30% on thick-walled beds). A bulk bag holds roughly 0.85m³ (~850kg topsoil). Allow soil to settle 10-15% and top up after the first few weeks. Mix topsoil with compost (roughly 2:1) for best results.