Topsoil calculator

DIY complexity

Beginner

Spreading topsoil is accessible manual work — a rake, wheelbarrow and some patience are enough, though achieving an even finished depth over an irregular lawn takes a bit of practice.

Introduction

This calculator estimates the volume, weight and purchase quantity of topsoil needed for a new lawn, a raised garden bed, levelling an existing lawn, or planting trees and shrubs. Topsoil behaves differently from a hard aggregate: a fresh, loose delivery settles and consolidates naturally over the following weeks as it beds in, rains on and is walked over, so the loose volume you order needs to exceed the finished depth you actually want once it has settled — the tool lets you capture that with a settlement allowance alongside ordinary waste. Quality and organic content also vary hugely by supplier: a screened, blended topsoil with added compost is a different product from an unscreened general-purpose fill, and the two are not interchangeable where root growth or lawn establishment matters. Required depth differs sharply by purpose too — a thin topping to level an established lawn needs only a few centimetres, a new lawn base needs considerably more, and a raised bed or a tree planting pit needs a deep, loose, often lighter-density mix. The calculator sums the net area of one or more measured zones, applies the depth for each, converts the resulting volume to weight using an editable bulk density, and rounds up to whole bags or a bulk delivery tonnage that respects your supplier's minimum load. It cannot verify soil quality, drainage, or whether you are actually excavating into subsoil rather than buying topsoil.

Quick answer

For a new 25 m² lawn at 10 cm target finished depth with a bulk density of 1200 kg/m³, 10% waste and a 15% settlement allowance for natural consolidation, the estimated weight is about 3795 kg (≈3.8 t) — roughly 152 bags of 25 kg, or about 3.8 t as a bulk delivery.

Calculation methodology

01Measure each area to be covered as one or more zones (rectangle, circle, triangle, trapezoid or a hand-drawn shape) and subtract any excluded areas such as paths or existing beds.
02Sum the net area of all zones and multiply each by its own target finished depth — a thin levelling topping needs only a few centimetres, a new lawn base needs considerably more, and a raised bed or tree pit needs far more still.
03Apply a waste percentage to cover spillage and uneven spreading.
04Apply a settlement (consolidation) percentage separately, because loose delivered topsoil settles naturally over the following weeks as it beds in, rains on and is walked or driven over — order more loose volume than the finished depth alone implies.
05Convert the resulting volume to weight using the bulk density of the specific topsoil blend you are buying, adjusted for a moisture percentage if the load is delivered wet.
06Round the weight up to whole bags, or to a bulk tonnage that respects the supplier's minimum delivery load, and compare the two purchase costs.

Formulas

volume_m3 = Σ(area_i × depth_i) × (1 + waste) × (1 + settlement)

Every measured zone's net area is multiplied by its own target finished depth and the results are added into a raw volume. That raw volume is then inflated for ordinary waste and, separately, for expected settlement, because loose delivered topsoil consolidates naturally over the following weeks and will end up shallower than it was tipped unless enough extra is ordered.

Variables

area_i = net area of zone i (m²)
depth_i = target finished topsoil depth entered for zone i (m)
waste = spillage and uneven-spreading allowance (%)
settlement = extra loose volume ordered to allow for natural consolidation over the following weeks (%)
volume_m3 = total volume to purchase (m³)

Rounding rule: This intermediate volume is not rounded; rounding only happens once weight is converted into whole bags or a bulk tonnage.

Limitation: The settlement percentage is a planning estimate, not a guaranteed outcome — actual consolidation depends on how the topsoil was handled and screened, how it is compacted or watered in, and local rainfall in the weeks after delivery, so treat the default as a starting point and re-check the finished depth once it has settled.

weight_kg = volume_m3 × density_kg_m3 × (1 + moisture); bags = ceil(weight_kg ÷ bag_kg); bulk_t = max(minimum_t, ceil(weight_kg ÷ 100) ÷ 10)

Volume is converted to weight using the bulk density of the specific topsoil blend, then increased for moisture if the load is delivered wet. The weight is rounded up to whole bags for small jobs, and separately rounded up to the nearest 0.1 tonne for a bulk order, with the supplier's minimum delivery load enforced as a floor.

Variables

density_kg_m3 = bulk density of the chosen topsoil blend (kg/m³)
moisture = weight increase for wet material at delivery (%)
bag_kg = weight of one bag
minimum_t = supplier's minimum bulk delivery load (t)
bulk_t = bulk delivery quantity to order (t)

Rounding rule: Bags are always rounded up to a whole unit; bulk tonnage is rounded up to the nearest 0.1 t and then raised to the supplier's minimum delivery load if that minimum is higher.

Limitation: 1200 kg/m³ is an editable example for a moderately screened topsoil, not a fixed constant — a loose, compost-rich raised-bed mix can be noticeably lighter, an unscreened or clay-heavy fill can be considerably heavier, and moisture content shifts the figure further; confirm it against your supplier's product data before ordering.

Inputs that matter

Target finished depthDiffers sharply by purpose: a levelling topping over an existing lawn needs only a few centimetres, a new lawn base needs considerably more, and a raised bed or tree planting pit needs far more still.
Settlement (consolidation) allowanceLoose delivered topsoil settles naturally over the following weeks as it beds in, rains on and is walked over — unlike a mechanically compacted aggregate, this happens gradually on its own, so under-ordering leaves a shallower finished depth than planned.
Bulk densityVaries with screening, organic content and moisture; a loose, compost-rich blend for a raised bed is meaningfully lighter than a dense, unscreened general fill.
Organic content and screening qualityScreened, blended topsoil with compost supports root growth and lawn establishment far better than unscreened or subsoil-contaminated fill — the two are not interchangeable even at the same depth and price point.
Planting typeA lawn needs only a thin, uniform layer; planting beds need a deeper, looser profile; trees need a very deep, localized volume concentrated in the planting pit rather than spread thinly over a wide area.
Bag size vs. bulk minimumSmall beds or top-ups are usually cheaper in bags; a new lawn or larger project crosses a threshold where bulk delivery is cheaper, but only once the supplier's minimum load is met.

Worked examples

Levelling topsoil for an existing 18 m² lawn

Topping up low spots and evening out a tired lawn before overseeding: 18 m² zone, 5 cm depth, screened topsoil at 1200 kg/m³, 10% waste for uneven raking, no settlement allowance since a thin topping is worked into the existing turf rather than left as a loose fresh layer, no moisture adjustment.

Raw volume = 18 × 0.05 = 0.9 m³. With 10% waste and 0% settlement: 0.9 × 1.10 = 0.99 m³. Weight = 0.99 × 1200 = 1188 kg. Bags (25 kg each): ceil(1188 ÷ 25) = 48 bags.

0.9 m³ is the theoretical topping volume, 0.99 m³ is the quantity after waste, and 48 bags is the final purchase figure. No settlement allowance was added because a thin topdressing worked into existing turf with a rake or the back of a lute is not left as a loose layer that consolidates on its own.

⚠ 5 cm is a light topdressing depth suited to levelling, not to establishing a new lawn from scratch — if the area needs a full new lawn base rather than a touch-up, use a much greater depth and add a settlement allowance.

New lawn base for a 25 m² garden area

A new lawn being seeded over cleared ground: 25 m² zone, 10 cm target finished depth, screened topsoil at 1200 kg/m³, 10% waste, 15% settlement allowance because the fresh loose layer will consolidate under rain and light foot traffic over the following weeks, and 5% moisture because the load is delivered slightly damp.

Raw volume = 25 × 0.10 = 2.5 m³. With 10% waste and 15% settlement: 2.5 × 1.10 × 1.15 = 3.1625 m³. Weight = 3.1625 × 1200 × 1.05 ≈ 3985 kg. Bags (25 kg): ceil(3985 ÷ 25) = 160 bags. Bulk: max(1.0, ceil(3985 ÷ 100) ÷ 10) = 4.0 t.

2.5 m³ is the theoretical volume at the target finished depth of 10 cm; 3.1625 m³ is the loose volume to order once waste and settlement are added; 3985 kg is the moisture-adjusted weight that drives both the 160-bag figure and the 4.0 t bulk figure. The extra volume beyond 2.5 m³ exists specifically so the lawn still measures close to 10 cm deep after several weeks of natural consolidation, not because of a calculation error.

⚠ 15% settlement is an editable planning assumption, not a guaranteed outcome — actual consolidation depends on how the topsoil was screened, how well it is watered and lightly compacted after spreading, and local rainfall; check the finished depth again a few weeks after laying and top up if it has settled further than planned.

Raised garden bed, 3 m², bag vs. bulk cost

A raised garden bed filled with a looser, compost-blended topsoil: 3 m² zone, 30 cm depth, bulk density 1100 kg/m³ for this lighter mix, 5% waste, no settlement allowance because the loose mix is intentionally left uncompacted for root growth, no moisture adjustment. Bags cost 7.00 per 25 kg bag; bulk topsoil costs 75 per tonne plus a 45 delivery fee, with a 1 t supplier minimum.

Raw volume = 3 × 0.30 = 0.9 m³. With 5% waste and 0% settlement: 0.9 × 1.05 = 0.945 m³. Weight = 0.945 × 1100 = 1039.5 kg. Bags: ceil(1039.5 ÷ 25) = 42 bags → 42 × 7.00 = 294.00. Bulk: max(1.0, ceil(1039.5 ÷ 100) ÷ 10) = 1.1 t → 1.1 × 75 + 45 = 127.50.

Buying 42 bags would cost about 294.00, while a 1.1 t bulk delivery including the flat delivery fee costs about 127.50 — bulk is cheaper here even for a fairly small raised bed, because the order already clears the supplier's 1 t minimum. For a smaller bed that fell well under 1 t, bags could instead work out cheaper once the fixed delivery fee is factored in — always compare both totals rather than assuming bulk always wins.

⚠ Changing the selected currency only changes the displayed symbol — it does not convert 7.00, 75 or 45 into a different currency's equivalent value. Enter current local supplier prices in the currency you have selected, and confirm sales tax and any delivery surcharge separately.

Reading the results

The result panel separates the net area you measured, the volume after waste and settlement, the moisture-adjusted weight, and the final whole-unit purchase quantity in both bags and bulk tonnage — each figure is larger than the last for a specific reason, not a rounding inconsistency. Bag cost and bulk cost are shown side by side with the lower of the two highlighted, so you can see which route is cheaper once your supplier's minimum delivery load is taken into account. Because topsoil settles gradually rather than being mechanically compacted on the day of delivery, treat the calculated depth as a target to re-check in the weeks after laying, not a figure that is guaranteed the moment the load is spread.

Common mistakes

Ordering only the target finished-depth volume with no settlement allowance, then finding the lawn or bed sits noticeably shallower a few weeks after delivery once natural consolidation has taken place.
Assuming topsoil is a single generic product, when organic content, screening quality and whether compost has been blended in vary hugely by supplier and materially affect lawn establishment and plant growth.
Using a shallow lawn-levelling depth for a raised bed or a bulk fill project, or the reverse — required depth differs sharply between a thin topdressing, a new lawn base, a planting bed and a tree pit.
Excavating on site and assuming the material dug up is usable topsoil, when it may in fact be subsoil once the thin organic layer has been removed — subsoil generally needs improving, not substituting, for topsoil.
Treating a bulk density figure suited to a dense, mineral-heavy fill as valid for a loose, compost-rich raised-bed mix, which is meaningfully lighter and would be under-costed or over-ordered by weight if the wrong figure is used.
Spreading a tree or shrub's topsoil thinly over a wide area instead of concentrating a deep, loose volume in the actual planting pit where the roots need it.

Adapting to your country

Topsoil naming, quality grading and typical bulk density all vary significantly by country and supplier — 'screened topsoil', 'multi-purpose topsoil', 'planting mix' and 'general fill' can describe products with meaningfully different organic content and density, so match the calculator's density assumption to the specific product on your local supplier's list rather than a generic label. Bag sizes commonly used for topsoil differ by country and product, and bulk minimum-delivery quantities vary by region and hauler. Selecting a different currency changes only the displayed symbol — it does not convert any price you have entered, so re-enter a current local price after switching currency, and confirm sales tax and delivery surcharges separately since they are not built into the calculator's cost output.

Limitations and verification

This calculator produces a planning estimate for volume, weight and purchase quantity — not a soil test, a landscaping contractor's quotation or a guarantee of the finished depth after settlement. It does not verify soil quality, drainage, pH, contamination, or whether ground excavated on site is genuinely topsoil rather than subsoil. Bulk density, settlement and moisture figures are editable examples that must be checked against your actual supplier's product before ordering, since organic content and screening vary significantly by product and region, and it does not confirm that a delivery lorry can access the site for a bulk order. Always re-measure the finished depth a few weeks after laying, since natural consolidation continues after delivery rather than finishing on the day the material is spread.

Last reviewed: 2026-08-25

Frequently asked questions

Why does topsoil need a settlement allowance when gravel just needs compaction?

Gravel is usually mechanically tamped or trafficked into its compacted thickness immediately, while loose delivered topsoil consolidates gradually on its own over the following weeks as it beds in, rains on and is walked over — so a settlement allowance covers a slower, natural process rather than an immediate mechanical one.

How deep should topsoil be for a new lawn versus a planting bed?

A new lawn base is typically shallower than a planting bed, and a planting bed is shallower again than the deep, localized volume a tree or large shrub needs in its own pit — always match the depth to the specific planting type rather than using one figure for the whole garden.

Is soil dug up on site the same as topsoil I would buy?

Not necessarily. The thin, organically rich surface layer is topsoil; below it is typically subsoil, which is denser, less fertile and generally needs improving rather than being substituted for purchased topsoil.

Why does bulk density vary so much for topsoil?

It depends on screening, organic and compost content, and moisture — a loose, compost-blended raised-bed mix is meaningfully lighter than a dense, unscreened general fill, so the density you enter should match the actual product, not a generic figure.

Does the calculator guarantee the lawn will be exactly the depth I entered after a few weeks?

No. The settlement percentage is an editable planning assumption based on typical consolidation, not a guarantee — actual settlement depends on the specific topsoil, watering, light compaction and local rainfall, so re-check the finished depth after it has settled.

How does the bag vs. bulk cost comparison work?

The calculator totals the cost of buying whole bags at your entered bag price against the cost of a bulk delivery at your entered per-tonne price plus any delivery fee, respecting the supplier's minimum bulk load, and highlights whichever total is lower.

Does changing the currency convert the prices I entered?

No. Changing currency only changes the display symbol and formatting; enter current local supplier prices in the currency you select.

Is the result enough to order topsoil directly without further checks?

No. It is a planning estimate. Confirm the topsoil quality and organic content suit your project, check the site's delivery access for a bulk load, and re-measure the finished depth on site once the material has settled.

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