Advanced options
Based on screened topsoil at about 1.5 tonnes per cubic metre (moisture varies this). Depth guide: 10cm to lay turf over existing soil, 15cm for new lawns from seed, 20-30cm for beds and borders, 30cm+ for vegetable beds.
What The Topsoil Calculator Works Out
- Volume: length x width x depth with the depth in metres. A 5 x 4m lawn area topped at 10cm needs 2 m3. Depth depends on the job: 10cm is enough to lay turf over existing ground, 15cm suits a new lawn from seed, beds and borders want 20 to 30cm, and raised vegetable beds 30cm or more.
- Weight: volume x density. Screened topsoil runs around 1.5 tonnes per m3 when moderately moist, so the example is about 3 tonnes. Topsoil is bought by volume but delivered and priced by weight.
- Bulk bags: the weight divided by the bag size, rounded up. Insist on BS 3882 certified soil near food growing, since it has been tested for contamination; general-purpose screened soil suits lawns and landscaping.
- Preparation: never spread topsoil over compacted or weed-infested ground without breaking it up first, or the new layer sits like a saucer and drains badly.
- Soil type (advanced): changes the density. Dry sandy soil is about 1.2 t/m3, wet or clay-heavy soil 1.7, a topsoil and compost blend about 1.0 and bagged peat-free compost only 0.6, so the tonnage for the same volume varies nearly three-fold.
- Bulk bag weight and settlement (advanced): enter your supplier's actual bag weight (800 to 1,000kg is common), and add 10% to 20% for settlement, because topsoil sinks after laying and watering and should be raked out proud of the final level.
- Number of areas (advanced): multiplies the volume for several identical beds or borders so you can order in one delivery.
- Cost in bulk bags vs loose (advanced): bags x your bag price against tonnes x the loose price. Bulk bags typically cost GBP 70 to GBP 120 depending on grade; loose loads by the tonne are cheaper once quantities climb but usually need a 5-tonne minimum and a place to tip.
- Equivalent in litres (advanced): the volume in litres and the number of 50L compost bags that would be needed, useful for raised beds and planters where bagged compost or soil is the realistic option.
- Wheelbarrow loads (advanced): a tonne of soil moves in about 25 to 30 barrow loads, which is worth contemplating before the lorry leaves it on the drive.
Source and further reading: Royal Horticultural Society.