About the Topsoil Calculator
Whether you are seeding a new lawn, laying turf, building raised beds or filling a border, the question is the same: how much soil do I need? The answer is area times depth — but loose topsoil does not stay the depth you spread it. It settles, and a bed filled to the brim in spring can sit two inches lower by summer.
This topsoil calculator works out the volume you need in cubic yards or cubic metres, adds a settling allowance, and shows the approximate weight for trailers, bags and bulk bags. It also gives the number of bags and an optional cost, and it tells you the usual depth of soil for lawns, beds and top-dressing.
How to Use the Topsoil Calculator
Choose feet and inches or metres and millimetres.
Pick the shape of the area — a rectangle, or a circle for a round bed — and enter its dimensions.
Enter the depth of new soil in inches or millimetres.
Choose screened topsoil or a topsoil and compost blend, which is lighter.
Leave the settling allowance at 15% unless your supplier advises otherwise.
Optionally, add the price per cubic yard or cubic metre.
How the Topsoil Volume Is Worked Out
area = length × width (or π × diameter² ÷ 4)
volume = area × depth × (1 + settling %)
weight = volume × bulk density (for bags and transport)Topsoil is normally sold by volume, so the volume is the headline. The weight is an estimate, because moisture and clay content change it a lot.
Step-by-Step Example
A new lawn 30 by 20 feet, 4 inches of topsoil, at 35 per cubic yard.
Area: 30 × 20 = 600 ft² (55.74 m²)
Depth: 4 in = 0.333 ft (0.102 m)
Volume: 600 × 0.333 = 200 ft³ = 7.41 yd³
Settling: 7.41 × 1.15 = 8.52 yd³ (6.51 m³)
Weight: 6.51 m³ × 1.3 t/m³ = 8.47 t = 9.33 US tons
Cost: 8.52 × 35 = 298.15In metric, a 10 by 5 metre area at 100 mm needs 5.00 m³, or 5.75 m³ with 15% for settling — about 7.5 tonnes, or nine 850 kg bulk bags.
How Deep Should Topsoil Be?
| Use | Typical depth |
|---|---|
| New lawn from seed or turf | 4–6 in / 100–150 mm |
| Flower and vegetable beds | 8–12 in / 200–300 mm |
| Top-dressing an existing lawn | ¼–½ in / 6–12 mm |
Grass roots mostly live in the top few inches, but a thin layer over compacted subsoil or rubble dries out fast and gives a patchy lawn. Vegetables and shrubs need more depth to root and to hold moisture. Top-dressing is different: it is a thin sprinkling worked into an existing lawn to level hollows and improve the surface, not a new layer of soil.
Why Topsoil Settles
Delivered topsoil is loose and full of air. Once it is raked, rolled, watered and walked on, the air is pushed out and it sinks — typically by 10 to 20% of its depth. If you order exactly the volume of the space, the finished bed ends up low and water collects in it.
The calculator adds 15% by default. Use more for very loose, screened soil going into deep raised beds, and less if the soil will be compacted in thin layers as it is laid.
Bags, Bulk Bags and Loose Loads
A cubic yard is 27 cubic feet: 27 one-cubic-foot bags, or 36 of the common 0.75 cubic foot bags. A cubic metre is forty 25 litre bags. Bags make sense for a raised bed or two, but they are expensive for a lawn.
Beyond a cubic yard or so, a bulk bag or a loose load is far cheaper. Loose soil should be spread soon after delivery, and covered if rain is forecast, because a wet heap is heavy to move and hard to rake level.
Spreading Topsoil Properly
Good soil badly spread still makes a poor lawn. A few steps make the difference.
Loosen the ground underneath. Fork or rotavate the existing surface before the new soil goes on, so the two layers blend instead of forming a hard line that roots and water struggle to cross.
Spread in layers. Rake out a few inches at a time and firm each layer lightly by treading or with a light roller. This settles the soil evenly and shows up hollows before the final level.
Set the final level with a rake. Aim for a smooth surface that falls gently away from buildings, so rain drains off rather than towards the walls.
Let it settle before seeding. If time allows, leave the soil a week or two and water it; any remaining dips appear and can be topped up before the seed or turf goes down.
Understanding Your Result
Topsoil needed is the headline volume, including settling.
Volume repeats it in cubic yards and feet, or cubic metres and litres.
Weight is an estimate for trailers, bags and bulk bags.
Area and depth confirms the measurements used.
Bags gives the number of small bags, and bulk bags in metric.
Cost multiplies the volume by your price.
Worth knowing lists the usual depths, or warns when soil for a lawn is too thin.
When Should You Use This Calculator?
Seeding or turfing a new lawn on bare or poor ground.
Filling raised beds for vegetables or flowers.
Levelling a garden before landscaping.
Top-dressing a lawn in spring or autumn.
Comparing a bulk load with bagged soil on cost.
Common Mistakes
Forgetting settling. Ordering the exact volume leaves beds low.
Reading 4 inches as 0.4 feet. It is a third of a foot.
Spreading too thin for a lawn. Under about 3 inches, grass struggles in dry weather.
Ordering by weight in the rain. Wet soil weighs more for the same volume.
Leaving a loose load uncovered, where rain turns it to heavy mud.