How much topsoil do I need?

Topsoil is sold by volume, so work in cubic metres. Measure the length and width of the area in metres and multiply them together to get the square metres. Then multiply by the depth in metres. A 5m by 4m lawn is 20 m2, and at 100mm (0.1m) that is 20 x 0.1 = 2 cubic metres.

To turn cubic metres into tonnes, multiply by 1.5, because topsoil weighs roughly 1.5 tonnes per cubic metre. So 2 cubic metres is about 3 tonnes. Suppliers quote both, so it helps to have your figure in metres and in tonnes.

If the area is an odd shape, break it into rectangles, work each one out and add them up. Round up at the end rather than down.

For a new lawn, whether you are turfing or seeding, aim for 100mm to 150mm of decent topsoil over a firmed base. Turf will root into 100mm, but 150mm gives a better buffer against drought and more for the roots to work into.

For planting borders, go deeper, around 300mm to 450mm, since shrubs and perennials need more root run. Raised beds and vegetable plots want the whole depth filled, usually 300mm or more. For top dressing an existing lawn you only need a few millimetres brushed in, so a little goes a long way.

A common trick on deep build-ups is to use a cheap fill material for the bulk, then cap the top 100mm to 150mm with screened topsoil that grass and plants will actually grow in. Borders are usually finished with a 50mm layer of bark over the soil once planted.

A bulk bag holds about 0.7 cubic metres, which is just over a tonne. At 50mm deep it covers roughly 14 m2, at 100mm about 7 m2, and at 150mm about 4.5 m2.

Some yards also sell loose tipped loads by the tonne. Those can suit very big jobs, but they need hard standing to tip onto and everything gets barrowed by hand. TopTurf supplies in bulk bags only, which are tidier and get set down where the driver can reach.

Worked example: that 20 m2 lawn at 100mm needs 2 cubic metres. Divide by 0.7 and you get just under 3, so order 3 bulk bags.

TopTurf sells one grade in one unit: screened topsoil at £70 a bulk bag. No grade tiers to weigh up. Work out your cubic metres, divide by 0.7 and that is your bag count.

If you are unsure between one bag and two, order the larger option. Spare topsoil always gets used levelling low spots, and a second delivery costs more than the soil you saved.

In the wider market you will see three broad grades. Economy fill is unscreened as dug soil for building up levels and landscaping, not for growing in. Use that sort of material as bulk fill, then cap it with a better grade.

Screened topsoil is passed through a screen to take out stones and debris. It is the general purpose choice for lawns, borders and levelling, and it is the grade TopTurf sells, at £70 a bulk bag.

Premium BS3882 topsoil is tested to the British Standard and shows up on high spec planting jobs. For a normal garden, decent screened topsoil does the same work without the certificate.

Add roughly 10 to 15 percent to your figure. Topsoil settles once it is spread and firmed, the ground is never perfectly flat, and you will always find a low spot to fill. It is cheaper to have a little left over than to come up short.

We supply screened topsoil in bulk bags at £70 each, delivered from Leigh. Delivery is from £20, worked out from your postcode and the size of the order.

If it is a new lawn, we also cut turf to order, and Barrow Landscaping can lay the lot, so the topsoil, the levelling and the turf are handled together. Lawn turf is £4 per m2.

Work out the area in square metres and multiply by the depth. A 20 m2 lawn at 100mm needs 2 cubic metres, which is about 3 bulk bags at 0.7 cubic metres each. For 150mm of soil the same lawn needs closer to 4 or 5 bulk bags.

A bulk bag holds about 0.7 cubic metres, which is just over a tonne. That covers roughly 7 m2 at 100mm deep, or about 14 m2 if you only need 50mm.

Economy fill is unscreened soil for building up levels and bulk landscaping, not for growing in. Premium BS3882 meets the British Standard for topsoil and shows up on high spec planting jobs. Screened topsoil sits in between as the general purpose soil, and it is the only grade TopTurf sells, at £70 a bulk bag.