Soil Calculator

This soil calculator tells you how much topsoil, garden soil or fill you need for any bed, border, lawn or low spot. Enter the shape and size of the area and the depth you want, and it returns the volume in cubic yards and cubic feet, the number of bags in the four most common US bag sizes, and an approximate weight so you can judge whether to haul it yourself or have it delivered. It includes a settling allowance by default, because loose soil always ends up lower than it starts.

How to use the soil calculator

1. Choose the shape. Pick rectangle for beds, borders and most lawn areas, circle for round beds and tree rings, and triangle for corner beds. For L-shaped or irregular areas, split the space into simple shapes and calculate each one.
2. Enter the dimensions in feet. Use decimals for partial feet: 6 inches is 0.5 feet and 3 inches is 0.25 feet. For a circle, enter the diameter, which is the full width across the middle.
3. Enter the depth in inches. This is the thickness of soil you want to add, not the depth of the hole or bed, unless you are filling it completely. The depth guide below has typical figures.
4. Set the number of identical areas. If you have four beds of the same size, enter the size once and set this to 4.
5. Adjust the settling allowance. The default of 10 percent suits ordinary topsoil. Raise it to 15 or 20 percent for loose mixes with a lot of compost, or lower it if the material is already compacted.
6. Read the results. Use cubic yards if you are ordering bulk, and the bag count for your preferred bag size if you are buying bags.

The soil volume formula

Every soil calculation is the same basic idea: area multiplied by depth gives volume. The only complication is units, because area is measured in square feet while depth is usually measured in inches. Dividing the depth by 12 converts it to feet so that the answer comes out in cubic feet.

Cubic feet = area (sq ft) × depth (in) ÷ 12
Cubic yards = cubic feet ÷ 27

The area formula depends on the shape:

• Rectangle or square: length × width.
• Circle: 3.1416 × radius × radius, where the radius is half the diameter.
• Triangle: base × height ÷ 2, where the height is measured straight out from the base to the opposite corner.

The calculator then adds your settling percentage and rounds each bag count up to the next whole bag.

Worked example: a long border

A front border is 20 feet long and 3 feet wide, and you want to add 6 inches of new topsoil. The area is 20 × 3 = 60 square feet. The volume is 60 × 6 ÷ 12 = 30 cubic feet. Adding 10 percent for settling gives 33 cubic feet, which is about 1.22 cubic yards, or 17 bags of 2 cubic feet each.

Worked example: a round flower bed

A circular bed is 8 feet across and needs 8 inches of soil. The radius is 4 feet, so the area is 3.1416 × 4 × 4 ≈ 50.3 square feet. The volume is 50.3 × 8 ÷ 12 ≈ 33.5 cubic feet. With 10 percent for settling, that is about 36.9 cubic feet, or 1.37 cubic yards.

Worked example: a corner bed

A triangular corner bed runs 6 feet along each fence. Treat one fence as the base and the other as the height. The area is 6 × 6 ÷ 2 = 18 square feet, and at 8 inches deep the volume is 18 × 8 ÷ 12 = 12 cubic feet before settling.

Worked example: lawn topdressing

Spreading a thin layer of soil over a 1,000-square-foot lawn is a very different job. At a quarter inch, the volume is 1,000 × 0.25 ÷ 12 ≈ 20.8 cubic feet, or about 0.77 cubic yards. At half an inch, it doubles to about 41.7 cubic feet, or 1.54 cubic yards. Small changes in depth make a big difference over a large area, which is why measuring first matters.

How deep should the soil be?

The right depth depends on what you are growing and what the soil underneath is like. These are typical depths for home gardens.

When you add soil over existing ground, avoid creating a sharp boundary between two very different soils. Water tends to stall where a light, loose soil sits on dense clay, which can leave roots waterlogged. Loosening the existing surface and mixing in the first part of the new soil helps the two layers blend.

Cubic feet, cubic yards and bags

Bulk soil is sold by the cubic yard, while bagged soil is sold by the cubic foot. One cubic yard is a cube 3 feet on each side, which equals 27 cubic feet. That is enough to cover 81 square feet at 4 inches deep, or 54 square feet at 6 inches deep.

This table shows how many bags make up one cubic yard in the common bag sizes.

Bag sizes vary by brand, and a bag that looks similar to another may hold less. Check the volume printed on the bag before relying on any count. Some potting mixes are labeled in quarts or dry liters rather than cubic feet. One cubic foot is about 25.7 dry quarts, or about 28.3 liters.

Bulk or bagged soil?

For small jobs, bags are convenient. They fit in a car, they are easy to move around the yard, and leftovers store neatly. For large jobs, bulk delivery is usually cheaper and much less work than opening dozens of bags.

To compare prices fairly, convert both to price per cubic foot:

• Bagged: divide the bag price by the bag size in cubic feet.
• Bulk: divide the price per cubic yard by 27, then add the delivery fee spread across the whole order.

Delivery fees and minimum orders change the math. For a single cubic yard, the delivery charge can be more than the soil itself, so bags may win. Once you need two or three yards or more, bulk usually comes out well ahead. Ask the supplier where they can drop the load. A pile on the driveway is easy for them, while a pile on the lawn can leave ruts. The soil bag calculator makes the comparison for you.

Which kind of soil to buy

The word “soil” covers several products that are not interchangeable. Choosing the right one matters as much as buying the right amount.

• Topsoil is the upper layer of natural ground, screened to remove rocks and debris. Quality varies widely by supplier. It is best for filling, leveling and building up lawns and in-ground beds. Ask whether it has been screened and where it came from.
• Garden soil is topsoil blended with organic matter such as compost or aged bark. It is a good choice for improving in-ground beds.
• Raised bed mix is a lighter blend designed to drain well in a contained bed, usually combining soil, compost and an aerating ingredient.
• Potting mix contains little or no actual soil. It is built from peat or coir, bark, perlite and similar ingredients so it stays loose in pots. It is too light and too expensive to fill large beds on its own.
• Fill dirt is subsoil with little organic matter. It is fine for filling deep holes or building up grade under the top layer, but plants struggle to grow in it directly.

If you plan to grow food, ask bulk suppliers whether their topsoil or compost is tested. A soil test from your Cooperative Extension office after the soil is in place will also show whether it needs lime, sulfur or fertilizer.

Why add extra for settling

Soil delivered loose in a truck or poured from a bag contains a lot of air. Once it is spread, watered and walked on, it compacts. Organic matter such as compost also breaks down over the season, so blends rich in compost lose more volume than plain topsoil.

As a general guide, allow about 10 percent extra for screened topsoil, and 15 to 20 percent extra for compost-rich garden soil and raised bed mixes. You can always rake a small surplus into another bed, but a shortfall shows up as a bed several inches lower than planned after the first heavy rain.

How heavy is a cubic yard of soil?

Soil is heavier than most people expect. A cubic yard of topsoil commonly weighs somewhere around 2,000 to 2,700 pounds, depending on how wet it is and how much sand or clay it contains. The calculator uses about 2,200 pounds per cubic yard (1.1 tons) for its weight estimate.

That weight matters if you plan to haul soil yourself. Many half-ton pickups have a payload rating well under the weight of a full cubic yard of moist topsoil, so check the payload on your door sticker before loading. Wheelbarrows typically hold 4 to 6 cubic feet, so moving one cubic yard takes roughly five to seven loads.

Common mistakes to avoid

• Mixing up inches and feet. Entering 6 as the depth in feet instead of inches multiplies the result by 12. The calculator takes depth in inches for this reason.
• Using outside dimensions for framed beds. Board thickness reduces the inside area. For a bed with 2-inch-nominal sides, subtract about 3 inches from each outside measurement.
• Forgetting to subtract obstacles. Large stones, stumps, paths and existing plants all take up space. For small obstacles, ignore them and treat the extra as a buffer.
• Buying potting mix to fill beds. It is light, drains fast and costs much more per cubic foot than garden soil or bulk mixes.
• Dumping new soil on compacted ground. Loosen the existing surface first so water and roots can move between the layers.

Frequently asked questions