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TOPSOIL CALCULATOR / HOW-IT-WORKS

A clear measure. A better order.

The arithmetic is simple. The assumptions deserve just as much care.

Start with area and added depth

For a rectangular space, area = length × width. For a circle, area = π × diameter² ÷ 4. For an irregular space, measure a suitable area or split it into separate sections. Multiply each area by its added soil depth and its quantity, then add the volumes. Do not count overlapping sections twice.

Depth means the layer you intend to add, not the total depth of existing soil. With uneven ground, a single average depth is an approximation; separately measured sections may be more useful.

Keep the units consistent

For square feet and inches: volume in ft³ = area in ft² × depth in inches ÷ 12. Divide ft³ by 27 to get yd³. Metric measurements use area in m² × depth in cm ÷ 100.

Apply an allowance once

Planning volume = measured volume × (1 + allowance ÷ 100). The default 10% is an editable example. It does not predict compaction, moisture or settlement. Confirm whether your supplier’s coverage describes loose or finished soil, and avoid applying an allowance twice.

Whole bags and supplier increments

Bags = round up(planning volume ÷ labelled bag volume). Bulk order = round up(planning volume in the chosen ordering unit ÷ supplier increment) × increment. Enter 0 as the increment to retain the unrounded planning volume.

Example: 20 ft × 10 ft at 3 in requires 50 ft³. With 10% extra, the planning volume is 55 ft³ = 2.037037… yd³. That needs 28 whole 2 ft³ bags, or a 2.25 yd³ bulk order when ordered in 0.25 yd³ increments. At $40 per yd³, the rounded bulk material cost is $90. At $4 per bag, the bag material cost is $112.

Weight requires a density

Weight in kilograms = planning volume in m³ × supplied bulk density in kg/m³. The calculator does not assume a universal soil density. It reports US short tons and metric tonnes separately. Weight is based on the planning volume before supplier-increment rounding; confirm the actual order’s load with your supplier.

Cost assumptions

Bulk material cost uses the rounded bulk order; bag material cost uses whole bags. Prices are values you enter in USD, not live quotes. Costs round to cents using half-up rounding. The optional delivery charge is applied equally to both comparison totals; use separate actual quotes before deciding how to buy. Tax, variable delivery rates, minimum orders and other charges are excluded.

Precision and supported limits

Rectangular and known-area calculations retain decimal inputs and conversions as exact fractions until bag, supplier-increment and cent rounding. Circular areas use π approximated to 50 decimal places. Display values are rounded for readability and are never fed back into purchase rounding. Unit switches preserve stored measurements, even when the visible conversion is rounded.

Use 1–30 separate areas, quantities of 1–1,000, positive dimensions no greater than 100,000 m, area no greater than 10 billion m², and planning volume no greater than 1 billion m³. Bag counts are limited to 1 billion. Prices and charges are limited to $1 billion each and whole cents. These are software bounds, not practical delivery recommendations.

Sources and soil selection

Conversions follow the international foot and SI relationships documented in the NIST Guide for the Use of the International System of Units. Choosing suitable topsoil is a separate question: University of Maryland Extension explains soil for raised beds and recommends asking suppliers about soil testing and origin. This tool is not a soil test or a growing-medium prescription.

Return to the topsoil calculator or report a calculation issue.

Last revised 2026-10-19.