The method in four steps
- Area in square feet. Rectangle: length × width. Circle: 3.14 × radius × radius. Triangle: base × height ÷ 2.
- Depth in feet. Divide inches by 12. Three inches is 0.25 ft; four inches is 0.333 ft.
- Cubic feet. Area × depth in feet.
- Cubic yards. Cubic feet ÷ 27. Then add about 10% for settling.
Steps 2 to 4 combine into one shortcut, because 12 × 27 = 324:
cubic yards = square feet × depth (inches) ÷ 324
The topsoil calculator runs this for you and also gives bags and tons. If you’d rather understand the numbers first, the examples below cover most real jobs.
Example 1: a rectangular bed
A new flower bed 12 ft long and 3 ft wide, with 8 inches of topsoil.
- Area: 12 × 3 = 36 sq ft
- Cubic yards: 36 × 8 ÷ 324 = 0.89 cubic yards (24 cubic feet)
- With 10% extra: about 0.98 cubic yards, so 1 yard, or 27 bags of 1 cubic foot
Example 2: a round bed
A circular bed around a tree, 6 ft across, with 4 inches of topsoil. (Keep soil away from the trunk itself; piling soil against bark can harm trees.)
- Radius: 6 ÷ 2 = 3 ft
- Area: 3.14 × 3 × 3 = 28.3 sq ft
- Cubic yards: 28.3 × 4 ÷ 324 = 0.35 cubic yards (9.4 cubic feet)
- With 10% extra: 10.4 cubic feet, so 11 bags of 1 cubic foot
Example 3: an L-shaped yard
A patch of yard shaped like an L, getting 4 inches of topsoil before seeding. Split it into two rectangles:
- Rectangle A: 30 × 20 ft = 600 sq ft
- Rectangle B: 15 × 10 ft = 150 sq ft
- Total area: 750 sq ft
- Cubic yards: 750 × 4 ÷ 324 = 9.26 cubic yards
- With 10% extra: 10.2 cubic yards, so order 10 to 10.5 yards depending on how your supplier sells it
Example 4: a triangular corner
A corner bed with two straight sides of 10 ft meeting at a right angle, filled 6 inches deep.
- Area: 10 × 10 ÷ 2 = 50 sq ft
- Cubic yards: 50 × 6 ÷ 324 = 0.93 cubic yards (25 cubic feet)
Example 5: uneven ground
A 40 × 20 ft area to be brought up to a level finish. The depth needed varies, so measure it at several evenly spaced points. Say the five readings are 2, 3, 4, 5 and 6 inches:
- Average depth: (2 + 3 + 4 + 5 + 6) ÷ 5 = 4 inches
- Area: 40 × 20 = 800 sq ft
- Cubic yards: 800 × 4 ÷ 324 = 9.88 cubic yards
Take more readings on bigger or bumpier areas. A string line or a long straight board helps you see the finished level.
Turning cubic yards into what you buy
| You have | To get | Do this |
|---|---|---|
| Cubic yards | Cubic feet | × 27 |
| Cubic yards | Tons, about | × 1.2 (range × 1.0 to × 1.4) |
| Cubic yards | 1 cu ft bags | × 27 |
| Cubic yards | 0.75 cu ft bags | × 36 |
| Cubic yards | 1.5 cu ft bags | × 18 |
| Cubic yards | 2 cu ft bags | × 13.5 |
So Example 1’s 0.98 cubic yards is about 1.2 tons, or 27 one-cubic-foot bags. More on weight in how much does a yard of topsoil weigh, and on bags in the bags of soil calculator.
Common mistakes
- Mixing inches and feet. Entering a depth of 4 where the formula needs 0.333 makes the answer twelve times too big. The shortcut above avoids this.
- Measuring the outside of beds. Boards take up space; measure the inside.
- Forgetting settling. Fresh topsoil sinks after rain. Order about 10% more, and more for deep fills.
- Comparing yards to tons. A per-ton price and a per-yard price aren’t the same thing. Convert before you compare quotes; the topsoil cost guide shows how.
- Ordering topsoil for the whole depth of a big fill. For deep fills, many people use cheaper fill material underneath and save topsoil for the top 4 to 6 inches where roots grow.
How much soil do I need for other jobs?
The method is the same for any soil, compost or mix; only the depth changes. Typical depths: 4–6 inches for a new lawn, 6–8 inches for a new garden bed, 1–2 inches of compost as a top-up, and the full depth of the box for a raised bed.
Questions gardeners ask
- What is the quickest way to work out how much topsoil I need?
- Square feet × depth in inches ÷ 324 = cubic yards. For 500 square feet at 3 inches: 500 × 3 ÷ 324 = 4.6 cubic yards.
- How many yards of topsoil do I need for 1,000 square feet?
- About 3.1 cubic yards per inch of depth: 6.2 at 2 inches, 12.3 at 4 inches and 18.5 at 6 inches, before any extra for settling.
- How do I measure an irregular area?
- Split it into rectangles, triangles and circles, work out each area, and add them together. For curves, a few rectangles that roughly follow the shape are close enough for ordering soil.
- Why do I need more topsoil than the calculation says?
- Loose soil settles once it is raked, firmed and watered, ground is rarely perfectly level, and a little is always lost when spreading. Ten percent extra is a sensible default.