The quick answer
If you already know the area and the depth you want, the quantity is straightforward:
Then multiply cubic metres by 1,000 to get litres.
A 50 m² lawn with a 100 mm (0.10 m) layer needs 5 m³, or 5,000 litres, before any allowance. The difficult part is not the multiplication — it is choosing a depth that suits the actual job and then matching the result to the supplier's real bag or loose-delivery specification.
Topsoil is not one universal material or package size
Topsoil is the upper layer of soil used to create or improve lawns, beds and growing areas. Bought-in topsoil can vary in texture, screening, organic content, moisture and intended use. That means two suppliers can describe different bag volumes or quote the same nominal weight for products that occupy different volumes.
For quantity planning, start with the physical space you need to fill. Volume is stable because it is set by the dimensions of the project. Only after you know the cubic metres should you translate that volume into litres, bags or an estimated weight.
Step 1: decide what the topsoil is doing
The right depth depends on the project and what already exists underneath. A new lawn over poor or missing topsoil is a different job from lightly correcting levels in an established border.
The RHS states that laying lawns needs at least 10 cm of topsoil. Rolawn's current topsoil calculation guidance describes 100–150 mm for many new lawn rootzones. Use the site condition and turf/seed supplier guidance to choose the actual figure.
The RHS gives about 20 cm or more as a guide for new beds. Larger shrubs, poor subsoil or a deliberately raised finished level can require more.
Do not automatically use a lawn or bed preset. Measure from the existing surface to the intended finished level in several places and work from an average or split the job into zones.
A raised bed is a contained growing volume, often filled with a mix rather than topsoil alone. Use the Raised Bed Soil Calculator for that job.
A depth can be horticulturally reasonable and still be wrong for the site if it leaves soil above paving, door thresholds, retaining edges or drainage details. Measure the level you actually have available.
Step 2: measure the real area
For a simple rectangle, multiply length by width. If the lawn or bed bends around a shed, patio or path, split it into simple sections rather than using the outermost rectangle and ordering soil for space you will never fill.
Our Garden Area Calculator handles rectangles, circles, triangles, L-shapes, multiple areas and exclusions. That is especially useful when a topsoil job covers several beds or when permanent features need to be deducted.
Step 3: turn area and depth into cubic metres
Depth has to be in metres before you multiply it by square metres. This is the most common unit trap.
Once depth is converted, the calculation is simply area × depth. A 30 m² bed at 150 mm gives 30 × 0.15 = 4.5 m³. Since 1 m³ equals 1,000 litres, the same volume is 4,500 litres.
What about tonnes?
Weight is useful when a supplier quotes loose topsoil by the tonne, but it should not replace the volume calculation. Topsoil bulk density varies with moisture, compaction and composition. Rolawn explicitly notes that bulk density varies and says to check product specifications where available.
The Topsoil Calculator therefore makes density editable. If a supplier gives you its own conversion or stated bulk density, enter that figure. If it does not, treat any weight result as an estimate rather than a product guarantee.
Bags, bulk bags or loose topsoil?
The best buying format depends on the volume, access and the supplier. Small retail bags are convenient for minor jobs; bulk bags reduce handling for larger gardens; loose tipped loads can make sense when the project is large and there is safe access for delivery.
The calculator lets you type your supplier's bag size. That is much safer than a page that silently assumes every “bulk bag” contains the same amount.
Should I add extra for settlement?
Freshly placed soil can settle as air spaces reduce and the surface is levelled, watered and used. Uneven existing ground also creates uncertainty. An allowance can therefore be sensible, but it should be a conscious choice rather than a hidden percentage.
Calculate the measured requirement first. Then decide whether you want additional material for levelling, settlement or measurement tolerance. The calculator keeps those two numbers separate so you can see exactly what the allowance changes.
Worked topsoil examples
10 m × 5 m = 50 m². Depth 100 mm = 0.10 m. Volume = 50 × 0.10 = 5 m³ = 5,000 L. A 10% optional allowance would make the ordering volume 5.5 m³.
50 mm = 0.05 m. Volume = 20 × 0.05 = 1 m³ = 1,000 L. With genuine 50 L bags, that is 20 bags before allowance.
Instead of measuring the whole garden, calculate each border's area and add them. If the combined area is 30 m² and the chosen depth is 150 mm, the requirement is 4.5 m³ or 4,500 L.
Topsoil for lawns and turf
For a new lawn, topsoil depth is only one part of preparation. The ground below also needs to be suitable and not heavily compacted. The RHS turf guidance recommends cultivating soil well below the immediate surface and allowing prepared ground time to settle. Bought-in topsoil should therefore be treated as part of the rootzone build-up, not as a thin cosmetic layer covering badly compacted ground.
If you are buying turf after preparing levels, use the Turf Calculator separately. Topsoil volume and turf roll count are related through area, but they are different ordering problems.
Topsoil for beds and borders
New beds generally need more rootable depth than a lawn. The RHS topsoil buying guide uses about 20 cm or more for new beds, while the exact requirement depends on what you are planting and what soil already lies underneath. If you are merely improving an existing bed, adding a thick layer of imported topsoil may not be the right solution; compost or another soil improver can be a different material with a different purpose.
That distinction is why Gardeners Toolkit keeps separate Compost and Mulch calculators instead of treating every brown garden material as interchangeable.
Topsoil for raised beds
Do not automatically fill a deep raised bed with topsoil from bottom to top. RHS guidance notes that raised-bed depth depends on what will be grown and describes mixes containing topsoil, organic matter and sharp sand for many beds. Deep beds can also use lower-value fill beneath the main growing layer in appropriate situations.
For quantity, calculate the enclosed bed volume first with the Raised Bed Soil Calculator, then decide what proportion of that volume should actually be topsoil based on the growing plan.
Seven mistakes that create bad topsoil orders
- Choosing depth because a calculator default says so. Defaults are starting points; site condition and the project decide the real depth.
- Ignoring finished levels. Check paving, edging, drainage and thresholds before importing soil.
- Measuring only the outer garden rectangle. Split irregular areas and deduct permanent exclusions.
- Mixing millimetres and metres. Convert the depth before multiplying.
- Calling every bulk bag a tonne bag. Check the supplier's actual litres, cubic metres or stated weight.
- Assuming one density. Moisture and composition affect weight; use supplier data for tonne conversions.
- Adding an allowance without knowing it. Keep measured volume and extra ordering tolerance visible as separate figures.
Before the delivery arrives
Quantity is only part of the order. For a large delivery, check where the soil can be placed, whether a pallet or tipped load can reach the site, how far it must be moved by hand and whether the finished area is ready to receive it. Those practical details can determine whether bulk bags or loose delivery make sense even when the calculated volume is identical.
Sources and how to use them
This guide uses standard geometry for the quantity calculations. Practical depth and soil-use guidance was checked against current pages from the Royal Horticultural Society, the RHS turf-laying guide, and Rolawn's current topsoil calculation guidance. These sources do not make every garden identical: use them to choose a sensible starting point, then apply your own site measurements and the specification of the topsoil you intend to buy.
Ready to turn the measurements into an order?
Use the calculator to keep the base cubic metres, litres, packaging conversion and optional allowance visible as separate figures.