Soil calculator guide

A soil calculation starts the same way as any other landscaping material: area in square feet times depth, converted to cubic yards or cubic feet. What makes soil specific is choosing the right type for the job, since garden soil, topsoil, and compost are often confused even though they serve different purposes and are priced and sold differently by most suppliers.

Garden soil versus topsoil versus compost

Topsoil is closer to natural mineral soil, sometimes screened to remove large rocks and debris, and is generally used to build up grade, fill low spots, or serve as a base layer before something else is planted. Garden soil is a blend, often topsoil enriched with compost or other organic matter, formulated to be planted into directly, which is why raised beds and new flower or vegetable beds typically call for garden soil rather than plain topsoil. Compost is different again: it is an amendment, usually worked into existing soil or applied as a thin top dressing rather than used as a bulk fill material on its own.

Typical depths for soil projects

Filling a raised bed usually calls for 8 to 12 inches of garden soil, matching the depth of the bed frame itself. Leveling a low spot in a lawn or preparing ground before seeding typically uses 2 to 4 inches of topsoil. A vegetable bed dug into existing ground might only need 4 to 6 inches of garden soil worked into the top of the native soil rather than a full depth replacement. Because these depths vary so much by project, checking the specific depth for your situation before calculating volume matters more for soil than for a more uniform material like mulch.

Worked example

A raised bed frame measuring 8 feet by 4 feet, filled 10 inches deep, is 32 square feet of area. At 10 inches deep, one cubic yard covers about 32 square feet, so this bed needs almost exactly one cubic yard of garden soil, and most gardeners round up slightly to account for settling once the soil is watered in and beds down over the following weeks.

Weight matters more for soil than you might expect

A cubic yard of topsoil or garden soil weighs roughly a ton, sometimes more when the soil is moist, which is worth knowing before ordering a delivery to a wooden deck, a trailer with a load limit, or any surface with a weight restriction. Moisture content changes this figure meaningfully: soil delivered right after rain can weigh noticeably more than the same soil delivered dry, so treat weight estimates as a starting point rather than an exact delivered figure.

Calculate your own numbers

The gravel and mulch calculator includes both topsoil and garden soil blend as separate material choices, each with its own density, so you can enter your bed dimensions and depth once and get cubic yards, cubic feet, and an estimated weight specific to the soil type you have chosen rather than a generic average.

Step by step measuring procedure

Measure the finished soil area, not the outside edge of a fence, wall, or bed frame. For a rectangular bed, measure inside length and inside width in feet. For an L shaped area, split the shape into two rectangles, calculate each one, then add the square footage. For a curved border, measure the longest length and the average width, then reduce the result by about 10 percent if the curve removes a clear corner.

Set the depth in inches after deciding the final finished height. If the soil will sit below a timber or metal edging, leave 1 inch of freeboard at the top so watering does not wash soil over the edge. If sod or mulch will be added later, subtract that layer from the available depth before ordering soil.

Convert depth from inches to feet by dividing by 12. Multiply length by width by depth in feet to get cubic feet. Divide cubic feet by 27 to get cubic yards. Add a small allowance only after the base number is known. For loose soil placed in a bed, 5 to 10 percent extra is usually enough. For deep fills over rough ground, 10 to 15 percent is safer because voids and settlement are larger.

Useful figures for ordering and placing soil

The figures below are practical field numbers for checking an order before calling a supplier. They are not a substitute for measuring the site, but they help catch results that are off by a factor of 10 or by a depth conversion error.

One cubic yard covers about 324 square feet at 1 inch deep, 162 square feet at 2 inches deep, 108 square feet at 3 inches deep, and 81 square feet at 4 inches deep. If a calculated order gives far more or far less coverage than these reference values, recheck the depth conversion before ordering.

Frequent mistakes and how to recover

Ordering by surface area only causes underfilled beds. Recovery is simple if the first delivery is level: measure the remaining depth, calculate only that missing layer, and order the balance. Do not guess from the original bed height after soil has been raked unevenly.

Forgetting settlement leaves raised beds low after watering. If the bed settles 1 to 2 inches, loosen the top few inches with a fork before adding more soil. Placing fresh soil on a compacted crust can create a shallow layer that dries faster than the material below it.

Spreading soil too thick over existing grass can smother the lawn. If more than about 1 inch was placed over living turf by mistake, rake part of it off within the same day if possible. For larger repairs, lift excess soil into low spots or future planting areas rather than washing it in with water.

Using fill where planting soil was needed is harder to correct. If plants are already installed, remove soil around the root zones and replace only the planting pockets. For empty beds, blend compost into the upper layer if appropriate for the project, but do not rely on a thin surface dressing to correct several inches of poor material.

Dumping soil in the wrong place adds labor quickly. A cubic yard may take 9 to 14 full wheelbarrow trips, depending on barrow size and how heavily it is loaded. Before delivery, set plywood on soft ground and choose a dump spot within 50 to 100 feet of the work area when possible. For broader material questions, see the FAQ.

Special cases that change the calculation

Raised beds on a hard base need drainage attention before volume is calculated. If the bed sits on concrete, leave room for any planned drainage layer and only calculate soil above that layer. If the bed is open to native ground, calculate the full inside depth unless part of the native soil will be loosened and blended.

Sloped ground should be measured by average depth, not by the shallow edge. Measure the planned depth at the low side and the high side, add the two numbers, and divide by 2. Use that average depth for the volume calculation. For example, a bed that needs 8 inches at one side and 2 inches at the other has an average depth of 5 inches.

Tree rings and narrow borders are often overestimated. For a ring, calculate the outside circle area, subtract the inside circle area around the trunk or open center, then apply the depth. Keep soil away from bark and root flare instead of filling tight against the trunk.

Bagged soil works for small areas but becomes inefficient for larger fills. Convert the bag volume to cubic feet, then divide the project cubic feet by that number. If the calculated result is dozens of bags, a bulk delivery may be easier to place, but the site access, storage space, and load limits still need to be checked before ordering.

Read next

• Sand calculator guide: Calculate how much sand a paver base, play area, or drainage layer needs, with typical depths, weight per cubic yard, and a worked example.
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• Rock calculator guide: Calculate how much river rock or decorative stone a bed, dry creek, or border needs, with typical depths, weight per cubic yard, and a worked example.