Topsoil Calculator
Cubic yards, tonnes, and bags of topsoil for a given area and depth
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What this calculator computes
The topsoil calculator estimates the volume and weight of topsoil needed to bring a garden bed, lawn, raised planter, or new-build landscape to a target depth. Inputs are the area (length × width or measured square footage of an irregular bed) and the desired finished depth, which depends on the planting application: 100–150 mm (4–6 inches) for new-lawn establishment over hardcore or compacted subsoil, 150–200 mm for vegetable beds over poor underlying soil, 300–450 mm for raised vegetable beds with no subsoil contribution at all, and 25–50 mm for dressing existing lawns. Bulk density of topsoil varies from about 1.1 t/m³ for screened sandy loam to 1.5 t/m³ for unscreened clay loam, with most landscape-grade screened topsoil sitting at 1.3 t/m³. The calculator returns volume in cubic yards, cubic metres, and cubic feet, and weight in tonnes and US tons, so the result can be cross-referenced against quarry quotes (typically by the cubic yard in the US) and landscaping-supplier quotes (typically by the tonne or 1-tonne bulk bag in the UK and EU). It also estimates bag count for projects sold in 25-litre or 50-litre bags. The bulk-bag economics matter: a 1-tonne bulk bag holds about 0.7–0.8 m³ of topsoil and is usually cheaper per cubic metre than retail bags, but the bag must be delivered by HIAB lorry and needs hard-standing access.
Calculator
The formula
Formula
volume = length × width × depth weight = volume × density
Worked example
When to use this calculator
Use this calculator before ordering topsoil for new lawn establishment, garden-bed creation, raised planter filling, lawn levelling, and any landscaping project where bare subsoil or hardcore needs covering with a planting medium. The most common scenarios are filling raised vegetable beds (where the full 300–450 mm depth gets the calculator's largest volumes), establishing new lawn after construction (where 100–150 mm over compacted subsoil is the standard), and topping up existing borders. The calculator returns geometric volume; add 10–15% for settlement after the first watering and frost cycle, and another 5% for delivery spillage on hand-barrow projects. For raised beds with no subsoil contribution, mix the topsoil 50/50 with well-rotted compost to improve drainage and fertility — order half the calculated topsoil and an equal volume of compost.
Common input mistakes
- Confusing topsoil with subsoil. Topsoil is the upper 100–300 mm of natural soil profile, dark in colour and high in organic matter, suitable for plant growth. Subsoil is the layer beneath, lighter in colour, with poor structure and minimal organic matter, suitable only for fill or as a base under topsoil. Ordering subsoil for a vegetable bed produces a poor growing medium and disappointed gardeners; the price difference reflects the difference in nutrient and structural quality.
- Using a single bulk-density figure across all topsoil types. Screened sandy loam runs about 1.1 t/m³, unscreened clay loam runs 1.5 t/m³, and conservation-grade enriched topsoil sits between at 1.3 t/m³. Using a single figure (1.3 typical) introduces 10–15% error on weight estimates, which matters when ordering by tonne.
Frequently asked questions
How deep should topsoil be for a new lawn?
New lawns need 100–150 mm (4–6 inches) of topsoil over a firmed and graded subsoil layer, deeper if the underlying ground is compacted hardcore from construction or if the lawn has heavy-traffic areas. Below 100 mm the grass roots reach into the subsoil and dry out quickly; above 200 mm the soil settles unevenly and creates dips after the first season. The figure should be calculated post-settlement, so order 110–120% of the geometric volume to absorb compaction.
How much topsoil for a raised vegetable bed?
Raised beds with no subsoil contribution need the full bed depth filled with topsoil plus compost — typically 300–450 mm depth. A 4 m × 1.2 m × 400 mm raised bed needs 1.92 m³ of growing medium, mixing topsoil 50/50 with compost gives a fertile, well-drained base. For vegetables specifically, double-digging in the first year mixes the topsoil with the underlying subsoil and reduces the depth needed; for permanent raised beds the full depth is required.
What is the difference between topsoil and compost?
Topsoil is mineral soil (sand, silt, clay) with 3–10% organic matter, used as the bulk planting medium. Compost is fully decomposed organic matter (90%+ organic) used as a soil amendment to add nutrients and improve structure. Most planting projects use a mix: 70% topsoil and 30% compost for established beds, 50/50 for newly built raised beds. Pure compost compacts and dries unevenly, and is rarely used on its own.
Should I order topsoil in bags or in bulk?
Bulk bags (1 tonne, around 0.75 m³) are typically half the per-cubic-metre cost of retail 25 L or 50 L bags, but require HIAB-lorry delivery and hard-standing access. Retail bags suit small projects (under 0.5 m³) where carrying bags through a house or up steps is necessary. Loose-tipped delivery from a quarry is cheapest of all for 5+ m³ projects, but requires driveway space for the tipper and a wheelbarrow plan to move the soil to the bed.
How much will topsoil settle?
Freshly delivered loose topsoil settles 10–15% in the first month under its own weight, watering, and frost cycles, and can settle a further 5% over the first year as organic matter mineralises. For lawn applications this means the soil delivered at a 150 mm height settles to about 130 mm after the first season; allow for this when calculating order quantity. Light compaction with a roller before turfing reduces post-settlement dips.