Topsoil Calculator

Background.

Three inches of soil does not sound like much until it is sitting on the driveway. Spread over a 30 by 20 foot patch of yard, three inches is 150 cubic feet. Add 10 percent for settling and spillage and the order is 165 cubic feet, or 6.11 cubic yards. At 1.2 tons per cubic yard that is more than seven tons of material, and in 1.5-cubic-foot retail bags it would be 110 bags, which is a lot of trips to the garden centre.

The arithmetic turns on one conversion that is easy to fumble. Depth is thought of in inches, the area is measured in square feet, and bulk soil is sold by the cubic yard, which is 27 cubic feet. A useful anchor: one inch spread over 1,000 square feet is about 3.09 cubic yards. Six inches over the same area is about 18.5 cubic yards, which is the "approximately 19 cubic yards" that Purdue Extension's guide to establishing a lawn from sod gives for a 6-inch layer. With that figure in your head you can check a supplier's quote without a calculator.

Weight is the slippery result. A cubic yard of soil can weigh around a ton or a good deal more, depending on how sandy it is, how much organic matter it carries and, above all, how wet it is after a week of rain. The density setting matters when a supplier sells by the ton or when you are working out whether a trailer can carry the load. If you are buying by the yard, it does not change the order.

What is topsoil calculator?

Topsoil is the upper layer of soil, the part that holds most of the organic matter and most of the roots. What is sold as topsoil varies widely: screened loam with stones and debris removed, unscreened soil straight from a site, or blends with added compost or sand. Quality is not guaranteed by the name, which is why Purdue Extension advises testing any topsoil brought in from off-site, just as you would test the soil already there. Ordering it is a volume problem: area times depth gives the space to fill, an allowance covers settling and loss, and the result is expressed in the units the soil is sold in. Weight comes from bulk density. The USDA Natural Resources Conservation Service defines bulk density as the dry weight of soil divided by its volume, pore spaces included, usually in grams per cubic centimetre; mineral particles are about 2.65, so a medium-textured soil with about half its volume as pore space comes to roughly 1.33. Soils rich in organic matter are lighter, sandy soils heavier. Delivered soil also carries water, so its weight per yard is higher than its dry bulk density alone suggests. The cheapest topsoil is often the soil already on site: if a project involves heavy regrading, Purdue advises stripping and stockpiling the existing topsoil first and spreading it back once the rough grade is set, which can shrink the order considerably.

How to use this calculator.

1. 01Enter the length and width of the area in feet. For an irregular area, work out the total square footage first, then enter it as the length with a width of 1 foot; the volume comes out the same.
2. 02Enter the depth of soil you want in inches, as a finished depth. For filling hollows, use the average depth across the area rather than the deepest point.
3. 03Set the allowance for settling, spillage and an uneven base; 10 percent is the default. If the supplier's yards are already quoted as settled or compacted volume, use less so the margin is not counted twice.
4. 04Enter the supplier's density in tons per cubic yard if you are buying by weight or checking a trailer's load, and the bag volume in cubic feet if you are buying bags (a 50-litre bag is about 1.77 cubic feet).
5. 05Enter the price per cubic yard for a material cost. The per-ton and per-bag price fields do not currently change any figure shown, so multiply the tons or the bag count by those prices yourself.

The formula.

The volume in cubic yards is Yd³ = L × W × (d ⁄ 12) × (1 + w) ⁄ 27. L and W are the length and width in feet, d is the depth in inches, so d ⁄ 12 is the depth in feet and L × W × d ⁄ 12 is cubic feet. The allowance w is written as a fraction, 10 percent being 0.10. Dividing by 27 converts cubic feet to cubic yards, since a cubic yard is a cube 3 feet on each side; NIST Handbook 133 lists the relationship.

Everything else is derived from the allowance-adjusted volume. Weight in tons is cubic yards × density. Bags are the adjusted cubic feet ÷ the bag volume, rounded up to a whole bag; with 1.5-cubic-foot bags, 18 make a cubic yard. Material cost is cubic yards × the price per cubic yard, using the exact fractional volume. If a supplier sells by weight, enter a price per ton and the cost is the estimated tons times that price; for bags, the whole bags times the price per bag. Leave the bag volume at 0 to skip bags altogether. Suppliers usually sell in whole or half yards, often with a minimum load and a delivery charge, so the invoice will rarely match it to the cent.

The density you enter is a weight per loose, delivered cubic yard, not the laboratory bulk density soil scientists measure. To compare the two, one gram per cubic centimetre equals about 0.8428 US tons per cubic yard; the 1.2-ton default corresponds to about 1.42 g/cm³, and a dry soil at 1.33 g/cm³ to about 1.12 tons. Water accounts for much of the difference between a dry pile and a wet one.

Settling is real. Loose soil sinks as it is watered and walked on, and Purdue's sod guide suggests allowing about a week for new soil to settle before the final grading, with irrigation or rain to help it along. The allowance covers that loss and the soil left on the tarp and the wheelbarrow.

A worked example.

Frequently asked questions.

References& sources.

1. [1]U.S. Department of Agriculture, Natural Resources Conservation Service (2008). "Soil Quality Indicators: Bulk Density." USDA NRCS.
2. [2]U.S. Department of Agriculture, Natural Resources Conservation Service (n.d.). "Web Soil Survey." USDA NRCS.
3. [3]U.S. Department of Agriculture, Natural Resources Conservation Service (n.d.). "Soil Health Assessment." USDA NRCS.
4. [4]National Institute of Standards and Technology (2026). "NIST Handbook 133, Appendix E: General Tables of Units of Measurement." U.S. Department of Commerce.
5. [5]Bureau International des Poids et Mesures (2019). "The International System of Units (SI Brochure), 9th edition." BIPM.