Raised Bed Soil Calculator

Raised bed soil volume is calculated as length × width × depth. A depth of 200–300 mm suits most vegetables and flowers; deeper beds (400–600 mm) are needed for root crops and fruit. The RHS recommends filling raised beds with a mix of topsoil (60–70%), compost (20–30%) and sharp sand or perlite (5–10%) for good drainage.

This calculator also estimates the timber or sleeper quantity needed to build the bed frame. Standard options include treated softwood boards (150 × 22 mm, stacked 2–3 high), railway sleepers (200 × 100 mm) and composite boards. Corner posts, screws and weed membrane are included in the materials list.

Enter the bed dimensions. The calculator shows soil volume in litres and bulk bags, plus a bill of materials for the frame. A 1.2 m × 2.4 m bed at 300 mm deep is a popular size — wide enough for a double row of plants but narrow enough to reach the centre from either side without stepping on the soil.

How much soil for a raised bed? Volume = length × width × depth. Standard sizes: 1.2m × 2.4m × 300mm = 0.86 m³ soil. 1.2m × 1.2m × 400mm = 0.58 m³. 0.6m × 2m × 300mm = 0.36 m³. Bulk bag (UK): 0.7-0.9 m³ = covers 1-2 standard raised beds. Top up annually: 25-50mm soil sinks/decomposes per year = 50-100L per bed (1-2 bags retail).

Raised bed depths by crop. Salad leaves and herbs: 150-200mm minimum. Carrots, parsnips, beetroot (deep roots): 300-450mm. Brassicas (broccoli, cabbage, kale): 300mm. Potatoes: 300-400mm. Tomatoes (single per bed): 300-400mm. Fruit bushes (blueberries, raspberries): 400-500mm. Children's beds: 400-600mm height (no bending). Optimum 'no-bend' height: 750-900mm for adult comfort.

UK raised bed materials. Treated softwood (pressure-treated pine/spruce): £40-£120 per 1.2 × 2.4m bed. Lifespan 8-15 years. Cedar/larch: £100-£300 per bed. Premium hardwoods (oak, sweet chestnut): £200-£500 per bed. Composite/recycled plastic: £150-£400 per bed. Galvanised metal: £80-£250 per bed (modern look). Brick: most expensive but permanent. DIY scaffolding boards: £30-£70 per bed (free if reclaimed).

Filling cost-effectively. Hugelkultur method: bottom 30-50% wood/branches (rots over years), upper 50-70% topsoil/compost. Saves 40-60% on filling cost. Lasagne method: alternate layers of cardboard, manure, compost, grass clippings. Free if you DIY. Cheapest filling: subsoil from excavation (free if doing landscaping); upper 200-300mm quality topsoil/compost. Sample 0.86 m³ bed: 0.5 m³ wood/subsoil + 0.36 m³ topsoil = £18-£40 filled.

Best vegetables for UK raised beds. High-yield: courgettes (1-2 plants per bed produces 8-15kg); tomatoes (5-10kg per plant); climbing French beans (3-5kg per plant); strawberries (perennial, easy). Easy: salad leaves (multiple cuts per year); radishes (4 weeks seed-to-harvest); spring onions; herbs (parsley, basil, coriander). Avoid: sweetcorn (low yield per area); pumpkins (massive space needed); cauliflower (fussy).