How to do it
- 1
Measure the area
Measure length and width in feet and calculate the area in square feet. Use the shape formulas below for circles, triangles, and other shapes.
- 2
Convert the depth to feet
If the depth is in inches, divide by 12 to get feet. For example, 6 inches is 0.5 feet.
- 3
Multiply for cubic feet
Multiply the area in square feet by the depth in feet to get the volume in cubic feet.
- 4
Divide by 27
Divide the cubic feet by 27 to get cubic yards. Add a waste allowance if your project needs one, then round up to order.
Formula
Cubic yards = area (sq ft) x depth (ft) / 27
This single method works for every shape once you know its area. The only thing that changes between shapes is how you calculate the area in the first step.
Area formulas by shape
Calculate the area in square feet with the matching formula, then apply the same volume steps: multiply by depth in feet and divide by 27.
- Rectangle or square
- Area = length x width
- Square footage and depth
- Cubic yards = square feet x depth (in) / 324
- A shortcut when you already know the area in square feet and the depth in inches.
- Circle
- Area = 3.14159 x radius x radius
- Triangle
- Area = 0.5 x base x height
- Trapezoid
- Area = (side A + side B) / 2 x height
- Rectangular border
- Area = outer length x outer width minus inner length x inner width
Worked example
A rectangular driveway base, 30 feet by 10 feet, 5 inches deep.
- 1Find the area: 30 x 10 = 300 square feet.
- 2Convert depth to feet: 5 / 12 = 0.417 feet.
- 3Find cubic feet: 300 x 0.417 = 125 cubic feet.
- 4Divide by 27: 125 / 27 = 4.63 cubic yards.
The driveway base needs about 4.63 cubic yards.
Worked examples
Square footage shortcut
A 450 square foot bed, 3 inches deep.
- 1Multiply area by depth in inches: 450 x 3 = 1,350.
- 2Divide by 324: 1,350 / 324 = 4.17 cubic yards.
The bed needs about 4.17 cubic yards.
Circle
A round patio 12 feet across, 4 inches deep.
- 1Radius is half the diameter: 6 feet.
- 2Area: 3.14159 x 6 x 6 = 113.1 square feet.
- 3Depth in feet: 4 / 12 = 0.333.
- 4Cubic feet: 113.1 x 0.333 = 37.7, then divide by 27 to get 1.40 cubic yards.
The round patio needs about 1.40 cubic yards.
Triangle
A triangular bed with a 10 foot base and 8 foot height, 3 inches deep.
- 1Area: 0.5 x 10 x 8 = 40 square feet.
- 2Depth in feet: 3 / 12 = 0.25.
- 3Cubic feet: 40 x 0.25 = 10, then divide by 27 to get 0.37 cubic yards.
The triangular bed needs about 0.37 cubic yards.
Trapezoid
A trapezoid with parallel sides of 12 and 8 feet and a height of 6 feet, 4 inches deep.
- 1Area: (12 + 8) / 2 x 6 = 60 square feet.
- 2Depth in feet: 4 / 12 = 0.333.
- 3Cubic feet: 60 x 0.333 = 20, then divide by 27 to get 0.74 cubic yards.
The trapezoid area needs about 0.74 cubic yards.
Multiple areas
Two rectangular beds: 20 by 4 feet and 12 by 4 feet, both 3 inches deep.
- 1First bed: 80 square feet x 0.25 feet = 20 cubic feet.
- 2Second bed: 48 square feet x 0.25 feet = 12 cubic feet.
- 3Add them: 32 cubic feet, then divide by 27 to get 1.19 cubic yards.
The two beds together need about 1.19 cubic yards.
The measurements you need
Every cubic yard calculation needs the same inputs: the dimensions that define the area, and the depth or thickness of the material. Measure in consistent units, usually feet for the area and inches for the depth, and convert as you go.
Keep the unrounded numbers while you work and round only at the end, so small rounding errors do not add up.
The method for any project
Once you have your measurements, the process is always the same:
- 1Calculate the area in square feet using the right shape formula.
- 2Convert the depth to feet by dividing inches by 12.
- 3Multiply area by depth to get cubic feet.
- 4Divide cubic feet by 27 to get cubic yards.
- 5Add a waste allowance, then round up to order.
Borders and combined areas
For a frame or border, find the area of the outer shape and subtract the inner shape that is left empty. For a project made of several parts, calculate the cubic yards for each part and add them together.
The cubic yard calculator supports borders and multiple sections directly, so you can combine an L shaped patio or a bed with several parts in one estimate.
Formula summary by shape
Use this quick reference to pick the right area formula:
| Shape | Area formula | Then |
|---|---|---|
| Rectangle | length x width | x depth in feet, / 27 |
| Circle | 3.14159 x radius x radius | x depth in feet, / 27 |
| Triangle | 0.5 x base x height | x depth in feet, / 27 |
| Trapezoid | (A + B) / 2 x height | x depth in feet, / 27 |
Waste allowance and rounding
A waste allowance is extra material added on top of the exact volume to cover spillage, compaction, uneven grade, and trimming. The right percentage depends on the material and the job, so choose a value that fits rather than a fixed number.
For ordering, round the final figure up so you do not run short during the work. Confirm the amount with your supplier before you buy.
Common mistakes
These errors cause most bad cubic yard estimates:
- Forgetting to convert depth from inches to feet
- Using area in square feet without including a depth
- Mixing measurement units within one calculation
- Rounding each dimension early instead of at the end
- Treating an irregular area as a single rectangle
- Confusing cubic yards with tons, which depend on density
Ordering checklist
Before you place an order, confirm that you have:
- Measured every part of the area and added them up
- Used a single consistent set of units
- Applied the depth your project actually calls for
- Added a sensible waste allowance
- Rounded up and confirmed the amount with your supplier
Frequently asked questions
- How do you calculate cubic yards?
- Find the area in square feet, multiply by the depth in feet, and divide the resulting cubic feet by 27. If the depth is in inches, divide it by 12 first.
- What is the cubic yard formula?
- Cubic yards equals area in square feet times depth in feet divided by 27. A common shortcut is square feet times depth in inches divided by 324.
- How do I figure cubic yards from inches of depth?
- Divide the depth in inches by 12 to get feet, then multiply by the area and divide by 27. Or use square feet times depth in inches divided by 324.
- How do I calculate cubic yards for a circle?
- Find the area with 3.14159 times the radius squared, multiply by the depth in feet, then divide by 27.
- How do I handle an irregular shape?
- Split it into simple shapes like rectangles and triangles, calculate the cubic yards for each, and add the results.
- How much extra should I order for waste?
- It depends on the material and project. Choose a waste percentage that fits your situation and confirm the final amount with your supplier.
- Should I round cubic yards up or down?
- Round up for ordering so you do not run short. Keep the exact decimal while planning.
- Can I just use a calculator?
- Yes. The cubic yard calculator applies these formulas for any shape and can combine several areas, but knowing the method helps you check the result.
Every formula on this page reduces to area times depth divided by 27, the exact cubic-foot-per-cubic-yard relationship. Examples are computed with the same engine that powers the calculators. See the YardCalc calculation methodology.
Results are planning estimates. Last reviewed 2026-06-16.