What this calculator works out
Enter the area you are covering and the depth you want, and this gives you the topsoil needed as a volume, a weight, a number of bulk bags and a number of 25-litre bags, plus the turf rolls to cover the same area.
Topsoil is the item people most often under-order, because the volumes involved are unintuitive. A small back lawn can easily need nine tonnes, which is more than most people picture when they imagine spreading a few inches of soil.
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Before you calculate
- Measure the area you are actually covering, not the whole garden. Break irregular shapes into rectangles and add them together.
- Depth matters more than people expect. Doubling the depth doubles the cost, and the difference between 100 mm and 150 mm across a small lawn is more than a tonne of soil.
- Topsoil is sold by volume or by weight, and suppliers switch between the two. You need the bulk density to move between them.
- Turf is perishable. Order it to arrive the day you intend to lay it, not before.
For turf, 100 mm of decent topsoil beneath it is the usual minimum. For a lawn from seed, 150 mm gives roots more to work with. For planting beds, 300 to 450 mm depending on what is going in. Less than 100 mm and the lawn will struggle in dry summers, because there is not enough soil to hold water.
How this calculator works
Area = length × width
Volume in m³ = area × depth in mm ÷ 1,000
With wastage = volume × (1 + wastage ÷ 100)
Weight in tonnes = volume × bulk densityBulk density is the weight of a cubic metre of loose material. Screened topsoil is typically 1.3 to 1.6 tonnes per cubic metre depending on how wet it is and how much clay it contains, which is a wide enough range to matter on a large order. Wet soil weighs considerably more than the same volume of dry soil, so a delivery after heavy rain will be heavier without containing more soil.
Turf is calculated from area alone. A standard rolled turf in the UK covers roughly one square metre per roll, though sizes vary between growers, so the roll count here is a guide to check against your supplier's own figure.
Worked example: a small lawn
An 8 m by 5 m lawn, laid to turf over 150 mm of topsoil, with a 10% allowance:
- Area: 8 × 5 = 40 m²
- Volume: 40 × 0.15 = 6 m³, plus 10% = 6.6 m³
- Weight at 1.4 t/m³: 9.24 tonnes
- Bulk bags at 0.7 m³: 10 bags
- Turf: 40 m² plus 10% = 44 rolls
Nine tonnes for a small back lawn surprises most people. It is worth pricing a loose tipped load against bulk bags at that quantity, because the price per tonne usually falls sharply once you are ordering by the lorry.
Common mistakes
- Confusing volume with weight. A cubic metre and a tonne are not the same thing, and suppliers quote both.
- Forgetting that soil settles. Freshly tipped soil compacts once walked on and watered. The wastage allowance covers this.
- Ordering turf too early. Rolled turf deteriorates within a couple of days, faster in warm weather. Prepare the ground first, then order.
- Measuring the whole garden. Subtract paths, beds and anything else that is not being covered.
- Assuming a bulk bag is a cubic metre. Most hold appreciably less, and sizes vary between suppliers.
- Ignoring access. Nine tonnes of soil arriving on a lorry needs somewhere to go, and a wheelbarrow route to where it is needed.
Frequently asked questions
How many bags of topsoil do I need?
It depends on the bag. A 25-litre bag holds 0.025 cubic metres, so forty of them make one cubic metre. Bulk bags vary from about 0.5 to 0.9 cubic metres depending on the supplier, which is why this calculator asks you for the size rather than assuming one. For anything over about two cubic metres, a loose tipped load is usually cheaper.
How much does a cubic metre of topsoil weigh?
Typically 1.3 to 1.6 tonnes, most often quoted around 1.4. Wet soil and soil with a high clay content sit at the top of that range. The figure matters when a supplier prices by the tonne but you have measured by volume.
What depth of topsoil do I need for turf?
At least 100 mm of good topsoil beneath the turf, and 150 mm is better on poor ground. The turf itself adds roughly 25 to 40 mm. Less than 100 mm and the lawn will suffer in dry weather because there is too little soil to hold moisture.
How many turf rolls are in a square metre?
Most UK growers supply rolls covering about one square metre each, so the roll count and the area in square metres are usually the same number. Roll sizes do vary, so check the figure with your supplier before ordering.
Should I add sand to heavy clay soil?
Not in small quantities. Adding a little sand to clay can make drainage worse rather than better. Well-rotted organic matter is the usual recommendation for improving clay structure, worked in over several seasons. For a new lawn on heavy clay, a layer of screened topsoil above the clay is more practical than trying to change the clay itself.
When is the best time to lay turf?
Autumn and spring, when the ground is warm enough for roots to establish but the weather is unlikely to dry the turf out. Summer laying is possible but needs daily watering. Avoid laying on frozen or waterlogged ground.
Is what I enter stored?
No. Figures are processed in your browser and never transmitted or retained.
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References
These organisations publish the guidance and figures behind this page.
- Royal Horticultural Society — guidance on soil preparation, turf laying and lawn establishment
- GOV.UK — rules on topsoil, waste soil movement and importing soil to a site
Sources are checked at publication and can change — how I choose and check references.