Calculating Yards of Concrete: Formula and Examples

To calculate yards of concrete, multiply the pour’s length, width, and thickness in feet, then divide by 27 to convert cubic feet to cubic yards. Enter those three measurements to get the concrete volume in cubic yards; the result is a planning estimate, so account for the shape of the pour and material lost during placement.

Formula

For a rectangular slab, volume in cubic yards = length × width × thickness ÷ 27, with all three dimensions expressed in feet. The calculator accepts thickness in inches and converts it to feet first:

V = L × W × (D ÷ 12) ÷ 27

• V is volume in cubic yards (yd³).
• L is length in feet (ft).
• W is width in feet (ft).
• D is thickness in inches (in).

There are 12 inches in a foot and 27 cubic feet in a cubic yard, because 3 feet × 3 feet × 3 feet = 27 cubic feet. One cubic yard is approximately 0.7646 cubic metres, and one cubic metre is approximately 1.30795 cubic yards. Keep the measurements in consistent units before applying the formula.

Worked Example

Using the calculator’s default dimensions—10 ft long, 10 ft wide, and 4 in thick—first convert the thickness to feet:

1. 4 in ÷ 12 = 0.3333 ft (one-third of a foot).
2. 10 ft × 10 ft × 0.3333 ft = 33.3333 ft³.
3. 33.3333 ft³ ÷ 27 = 1.2346 yd³.

Rounded to two decimal places, the calculator returns 1.23 yd³, with a helper result of 33.33 ft³. The unrounded calculation is 10 × 10 × (4 ÷ 12) ÷ 27 = 1.2345679 cubic yards.

How to Measure and Use the Result

Measure the area that will actually contain concrete, not just the outside dimensions of a form if the shape or edges vary. For a slab, use the planned length and width and the specified thickness. For a rectangular footing or curb, calculate each distinct section separately if its dimensions differ, then add the volumes.

• Slab: length × width × thickness.
• Rectangular footing: length × width × depth.
• Several separate pours: calculate each section’s volume and add the results.
• Round column: use π × radius² × height, with dimensions in feet, then divide cubic feet by 27.

The result is a volume, not a weight. Concrete is commonly ordered by the cubic yard in the United States; elsewhere, cubic metres may be more familiar. If converting a metric design, convert every dimension to the same unit before calculating. For example, a slab measuring 3 m × 3 m × 0.1 m has a volume of 0.9 m³, approximately 1.18 yd³.

Irregular Shapes, Openings, and Multiple Sections

Many real pours are not perfect rectangular prisms. Divide the layout into simple shapes whose volumes you can calculate, then add the pieces. For a nonuniform slab, measure its sections or use a suitable average thickness only when that average reasonably represents the actual design. A sloping surface, rounded edge, thickened perimeter, or stepped footing may need separate calculations.

Subtract a large, defined opening that will not receive concrete—for example, a substantial pit or void included inside the measured outline. Small reinforcement bars and ordinary embedded items are not generally worth subtracting from a practical order estimate. Do not subtract an opening if it is already excluded from the measured dimensions.

Ordering Quantity and Common Mistakes

The geometric calculation estimates the volume needed to fill the measured space. The amount to order may need a modest allowance for uneven excavation, form dimensions, spillage, and concrete left in equipment. The right allowance depends on how accurately the site and forms are prepared; do not treat a fixed percentage as suitable for every job. For a large pour, confirm dimensions, mix requirements, delivery quantity, and ordering increments with the concrete supplier or project professional.

• Mixing units: multiplying feet by inches without converting produces the wrong volume. Convert thickness to feet, or convert all dimensions to inches and divide cubic inches by 46,656.
• Confusing square and cubic units: area is measured in square feet; concrete quantity is a three-dimensional volume, such as cubic feet or cubic yards.
• Rounding too early: keep extra digits through the calculation and round the final result. The displayed two-decimal result is not as precise as the input measurements.
• Assuming exact site dimensions: check the prepared base and forms at multiple points, especially where depth or ground level varies.
• Using the wrong thickness: a small depth error across a large slab can change the total volume substantially.

Concrete volume calculations do not determine the required mix strength, reinforcement, joint layout, base preparation, or structural dimensions. Those depend on the design and intended use; use the project specifications rather than choosing them from a volume estimate.

Frequently Asked Questions

How many cubic feet are in a yard of concrete?
One cubic yard contains 27 cubic feet. To convert cubic feet to cubic yards, divide by 27; to convert cubic yards to cubic feet, multiply by 27.

How do I calculate concrete for a 10-by-10 slab?
Include the slab thickness. At 4 inches thick, the calculation is 10 × 10 × (4 ÷ 12) ÷ 27, which is about 1.23 cubic yards before any ordering allowance.

Should I order exactly the calculated amount?
Not automatically. The calculation assumes the measured dimensions describe the finished space exactly. Site variation, spillage, and placement conditions can affect the amount needed, so consider the project’s uncertainty and confirm the order with the supplier.

Can I calculate concrete in inches?
Yes. Multiply length, width, and thickness in inches to get cubic inches, then divide by 46,656, the number of cubic inches in a cubic yard. Converting thickness to feet is often simpler for measurements taken in feet.

How do I calculate a round concrete column?
Use the cylinder formula: π × radius² × height. Measure radius and height in feet to get cubic feet, then divide by 27 for cubic yards. If you measured the diameter, divide it by two to find the radius.

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in length | Length | ft | 10 | 0
in width | Width | ft | 10 | 0
in depth | Thickness | in | 4 | 0
out yards | Concrete volume | yd³ | length * width * (depth / 12) / 27 | 2
out feet | Concrete volume | ft³ | length * width * (depth / 12) | 2