Topsoil Calculator — Tonnes & Cost

Topsoil quantity is calculated as area multiplied by depth and then converted to tonnes. Loose topsoil has a bulk density of roughly 1.3 to 1.5 t/m³. A new lawn wants a minimum depth of 100 to 150 mm, raised beds typically need 200 to 300 mm, and border improvement needs 50 to 100 mm worked into the existing soil. Levelling an established lawn takes far less, at 25 to 50mm as a top dressing.

Topsoil quality in the UK is graded to BS 3882. General-purpose topsoil suits most garden uses, while premium topsoil is screened to a finer grade for lawns and turf laying. The calculator shows volume in cubic metres, weight in tonnes and the number of bulk bags, a standard bulk bag holding approximately 0.6 m³ or 0.8 to 1.0 tonnes. Enter the area and the depth you want and it also gives an estimated delivered cost, at £30 to £55 per tonne for general purpose and £45 to £70 per tonne for premium screened.

Working in cubic metres per square metre makes the arithmetic quick. Levelling a lawn at 50mm needs 0.05 m³/m², a new lawn over poor soil at 100mm needs 0.1 m³/m², and a raised bed at 200mm needs 0.2 m³/m². A 50 m² lawn topped with 50mm therefore takes 2.5 m³, or about 3 bulk bags at 0.7 to 0.9 m³ each, with a bag weighing roughly 875 kg at a topsoil density of 1.25 tonnes per m³. For large areas a loose tipper load of 10 m³ or more works out much cheaper per cubic metre, but it needs vehicle access and somewhere to tip it.

Prices in 2026 separate the grades clearly. Screened general purpose topsoil that complies with BS3882 runs £35 to £60 per m³ delivered. Premium topsoil low in stone and clay is £60 to £100, a free-draining loam mix £55 to £90, and vegetable garden topsoil with high organic matter £70 to £120. Subsoil is cheaper at £20 to £40 but suits bulk filling only, never planting. Treat unusually cheap topsoil with suspicion, since it is often subsoil or contaminated waste. Check the supplier's credentials and ask for a soil analysis if you are buying 10 m³ or more.

Knowing what you already have is worth the modest cost of testing. NRM Laboratories or the RHS will analyse a sample for £20 to £40. The common British soils each behave differently: clay is heavy and fertile but slow-draining with an alkaline tendency, sandy soil is light and free-draining but low in nutrients and inclined to acidity, loam sits in the ideal middle, and peat is acidic and water-retentive. Vegetables want a pH of 6.0 to 7.0, lawns 5.5 to 7.0, and ericaceous plants such as rhododendrons and blueberries 4.5 to 5.5. Calcified seaweed at £15 to £25 per 25kg raises pH, while sulphur or a pine needle mulch lowers it.

Depth requirements for raised beds follow the roots. Vegetables want a minimum of 300mm, with 400 to 450mm ideal for carrots, parsnips and other root crops. Salad and herbs manage on 200mm, fruit bushes want 400 to 500mm, and a lawn over hard subsoil needs 100 to 150mm for healthy root growth. A standard 1.2m by 2.4m bed filled to 300mm takes 0.86 m³, which is about one bulk bag. Mixing in 25% compost gives a richer growing medium. Beds sink as organic matter decomposes, so expect to top up by 25 to 50mm each year.

Sourcing rewards a little planning. If you are excavating for foundations, a basement or a pond you will generate surplus soil, so strip and stack the top 200 to 300mm separately, because that is the valuable layer and the subsoil beneath it is useless for planting. Soil swap groups on Freecycle and Olio often list free soil if you collect, and a seller in the same area saves the delivery charge. Garden centres charge two to three times builder's merchant prices for bagged multi-purpose topsoil, so for anything above 2 m³ buy a bulk bag or a loose load from a soil supplier.