GardenCalcs.uk
Raised Bed Material Calculator , Build Your Own Raised Beds
Calculate all the materials needed to build raised garden beds.
Outside-to-outside length. A 2.4m sleeper sets a tidy length with no cutting
Keep to 1.2m or less so you can reach the centre from both sides without standing on the soil
200-300mm suits most veg; 400mm+ for carrots and parsnips; 600-700mm for no-bend access
Use untreated larch, oak or cedar for edibles; avoid old tanalised timber and railway sleepers
Multiplies every quantity; leave a 600mm path between beds for a wheelbarrow
Extra for cuts and overlap joints (default 10%)
For timber beds: 75mm or 100mm square posts
How We Calculate This
This calculator works out material quantities from bed dimensions, construction material, and number of beds.
Calculations
- Courses high = Bed height / course height (rounded up). For brick and stone the course height adds a 10mm mortar joint, so a 65mm brick coordinates to a 75mm course, so four courses make 300mm.
- Material count: timber is CUT FROM STOCK, so we build the list of pieces the bed needs (two lengths and two widths per course, with any side longer than one board split into whole boards plus a remainder) and pack that list into as few boards as possible, largest piece first. Offcuts therefore serve other sides and other courses, which is why four short 0.5m ends come out of a single 2.4m sleeper rather than costing four. Bricks and stone are laid to a module instead of being cut from stock, so those repeat every 225mm (215mm brick + 10mm perp joint) around the perimeter, times the number of courses. The waste allowance is applied to the result.
- Landscape fabric = (Base area + side area) x (1 + overlap%)
- Soil volume = Internal length x internal width x height, where the internal dimensions subtract twice the wall thickness , this fills the actual cavity rather than the external box.
- Corner posts = 4 internal posts the full bed height; the total is given in linear metres of your chosen 75mm or 100mm square section.
- Bulk bags = Soil volume / 0.85 m3 per bag (a bulk bag holds ~0.85 m3 / ~850kg)
Frequently Asked Questions
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.
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Last updated: March 2026
All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.