How much topsoil do I need?

1. The calculation, step by step

Topsoil is a pure volume problem. Measure the area, decide the fill depth, multiply, then convert to the unit your supplier sells in — bulk cubic yards (or cubic metres) or bagged by the bag.

1. Measure the area. Length × width in feet (or metres). For an irregular shape, split it into rectangles and add the volumes, or estimate a rough oval as length × width × 0.8.
2. Multiply by depth. Convert depth to the same unit first — 4 inches = 4 ÷ 12 = 0.333 ft. Area × depth in feet = cubic feet; divide by 27 for cubic yards. Metric: metres × metres × metres gives cubic metres directly.
3. Convert to bags. Each standard 40 lb North-American bag holds 0.75 cubic feet, so bags = cubic feet ÷ 0.75, rounded up. One cubic yard = exactly 36 bags. For metric bags, divide cubic metres by the bag size in cubic metres (a 35 L bag = 0.035 m³, so 1 m³ = 29 bags).

Worked example — a 20 ft × 10 ft lawn strip to be top-dressed to 4 inches: volume = 20 × 10 × (4 ÷ 12) ≈ 66.7 cubic feet; 66.7 ÷ 27 ≈ 2.5 cubic yards. In standard 40 lb bags: 66.7 ÷ 0.75 = 89 bags. At that quantity, a single bulk delivery is almost certainly the cheaper option.

2. Topsoil coverage table

Pure geometry — coverage = area × depth. These are exact figures for a flat, even fill. Real ground is rarely perfectly level, so adding 5–10% to your order is sensible on larger jobs.

At 4 inches (100 mm) — new lawn, top-dressing

At 6 inches (150 mm) — raised beds, deep lawn renovation

Cu yd values are rounded; bag counts are computed from the exact cubic-feet volume, then rounded up. Multiplying the displayed cu yd × 36 may differ by one bag on edge cases.

Metric users: a cubic metre is 1,000 litres. At 100 mm (10 cm) deep, one square metre of area uses exactly 0.1 m³ of topsoil — so a 3 × 3 m bed needs 0.9 m³, which is 26 bags at 35 L each.

3. How deep should topsoil be?

Depth changes the job cost more than anything else — doubling the depth doubles the topsoil order, so it is worth choosing carefully. These are widely-used horticultural guidelines, not code values: actual requirements depend on your soil, drainage and what you are planting.

• Overseeding or light top-dressing: ¼–½ inch (6–12 mm). Enough to fill low spots and cover seed without smothering the existing lawn. Volume is tiny — usually bags only.
• New lawn from seed or sod: 4–6 inches (100–150 mm) is the commonly recommended minimum for grass roots to establish in good growing medium. Below 4 inches, roots hit hard sub-grade sooner and the lawn struggles in dry spells.
• Flower and shrub beds: 6–8 inches (150–200 mm) gives most perennials and shrubs a solid root zone. Shallower works for annuals; deeper is better if the sub-grade is very poor or compacted.
• Vegetable garden or raised bed: 8–12 inches (200–300 mm) of quality growing medium is the practical target for most vegetables. Deep-rooting crops like carrots and parsnips benefit from the full 12 inches.
• Filling behind retaining walls or levelling a slope: however deep the finished grade requires — but use sub-grade fill to bring rough levels up cheaply, then top the last 4–6 inches with quality screened topsoil for planting.

One practical note: topsoil settles after laying, especially if it is freshly delivered and loose. On larger jobs, expect 5–10% settlement over the first season — either add that margin to your order or plan a light top-up in spring.

4. Bags, bulk bags, or bulk delivery?

The volume of topsoil is the same whether it arrives in bags or by the lorry — the choice is really about handling and price.

• Bags are tidy and easy to carry through a gate or house. They suit small jobs — up to about half a cubic yard (roughly 18 bags). Above that, the handling effort and cost per yard start to add up.
• Bulk or jumbo bags ("dumpy bags" / "bulk bags"): typically hold 0.5–1 m³ (around 0.7–1.3 cubic yards). A 1 m³ bulk bag holds as much as about 29 standard 35 L bags — usually cheaper per m³ than individual bags and easier to move with a fork truck or loader.
• Loose bulk delivery is the cheapest per yard but needs a clear access point for a tipping truck and somewhere to tip. Once the pile is down, you move it by wheelbarrow or loader. For anything over two or three yards, loose bulk is almost always the most economical choice.

The break-even for US buyers is roughly 12–14 bags versus the cost of a cubic yard delivered locally. Past that point, price up a bulk yard and compare. The calculator shows both the cubic yards and the bag count so you can run that comparison directly.

5. Which type of topsoil should I buy?

Not all topsoil is the same. Buying the wrong grade is the most common mistake — cheap fill looks like topsoil but will not grow much.

• Screened topsoil has been sieved to remove rocks, roots and large debris. It is the standard grade for lawns and beds — fine enough to rake, mix with seed and lay sod on. This is what the calculator is sized for.
• Premium or blended topsoil is screened topsoil mixed with compost, sand or other amendments to improve structure, drainage and organic content. It costs more but is the better choice for vegetable gardens and new lawns on poor sub-grade.
• Unscreened or sub-grade fill is cheap and useful for bulk raising of levels — behind retaining walls, under patios or filling low spots before topping with good soil. It is not a planting medium on its own.
• Compost or growing medium is not the same as topsoil, though the terms are sometimes used loosely. Pure compost is too rich and drains too quickly to use alone in depth; blended 50/50 with screened topsoil it makes an excellent raised-bed mix.

A quick tip: ask your supplier for the organic content and pH. Good screened topsoil typically has 3–8% organic matter and a neutral pH (around 6.5–7.0). If you are starting a lawn, that range gives grass the best start without amendments.

Common questions

How do I calculate how much topsoil I need?

Volume = length × width × depth, with depth in the same unit as length and width — 4 inches is 0.333 feet. The result is cubic feet; divide by 27 for cubic yards. Each 40 lb bag holds 0.75 cubic feet, so bags = cubic feet ÷ 0.75, rounded up. The calculator on this page does all of that in one step.

How many 40lb bags of topsoil equal 1 cubic yard?

A cubic yard is 27 cubic feet. A standard 40 lb bag of topsoil holds 0.75 cubic feet, so 27 ÷ 0.75 = 36 bags exactly. That is the conversion worth memorising when you are weighing bags against bulk delivery pricing.

How many wheelbarrows is 1 yd of topsoil?

A standard contractor wheelbarrow holds about 3 cubic feet of loose material. One cubic yard is 27 cubic feet, so that works out to 9 full wheelbarrow loads. A smaller garden wheelbarrow (around 2 cubic feet) takes roughly 13–14 loads for the same yard.

How many bags is 10 yards of topsoil?

10 cubic yards × 36 standard 40 lb bags per yard = 360 bags. At that scale, bulk delivery from a landscape supplier is almost always cheaper than buying bags — compare the per-yard delivered price against 36 times the bag price to find the break-even.