Concrete Volume Calculator - Calculate Cubic Meters & Yards

What is a concrete volume calculator?

A concrete volume calculator finds how much concrete a slab, footing, or driveway needs. It multiplies length, width, and depth to get a volume, then shows that volume in cubic meters or cubic yards. Builders use the result to order the right amount of ready-mix concrete or the right number of bags of dry mix.

Concrete volume formula

Concrete volume follows a simple rule for any rectangular pour:

Volume = Length × Width × Depth

All three measurements must use the same unit before multiplying. In the metric system, enter length, width, and depth in meters, and the result comes out in cubic meters (m³). In the imperial system, enter all three in feet. The calculator multiplies them to get cubic feet, then divides by 27 to convert to cubic yards (yd³), the unit concrete suppliers in the United States use for ordering.

How to calculate concrete volume

1. Measure the length and width of the area to be poured.
2. Decide the depth, also called thickness. A patio or sidewalk is often 10 cm (4 inches) thick. A driveway is often 10–15 cm (4–6 inches) thick. A foundation slab is often 15–20 cm (6–8 inches) thick.
3. Multiply length × width × depth using one consistent unit.
4. Convert the result to cubic yards if concrete will be ordered by the yard, which is standard in the United States.
5. Add extra concrete for waste, explained below.

Worked example

Metric. A patio measures 4 m long and 3 m wide, poured 0.1 m (10 cm) deep.

Volume = 4 × 3 × 0.1 = 1.2 m³

Imperial. A driveway measures 12 ft long and 9 ft wide, poured 0.5 ft (6 inches) deep.

Volume = 12 × 9 × 0.5 = 54 ft³

Cubic yards = 54 ÷ 27 = 2 yd³

The driveway needs 2 cubic yards of concrete before any waste allowance is added.

Cubic meters and cubic yards

A cubic meter is a cube 1 meter on each side. A cubic yard is a cube 1 yard (3 feet) on each side. One cubic meter equals about 1.31 cubic yards, and one cubic yard equals about 0.765 cubic meters. Concrete is sold by the cubic yard in the United States and by the cubic meter in most other countries, so knowing both units matters when ordering from a supplier that uses a different system.

How much extra concrete to order

Concrete suppliers and contractors commonly add 5–10% to the calculated volume. This buffer covers uneven ground, formwork that is slightly larger than planned, and spillage during the pour. A project that calculates to 2 cubic yards would typically be ordered as 2.1 to 2.2 cubic yards.

Converting volume to bags of concrete mix

Small jobs, such as fence posts or a short garden path, often use bagged concrete mix instead of a delivery truck. Bag coverage is printed on the packaging, but typical figures are:

• 80 lb bag: about 0.6 cubic feet, or about 0.017 cubic meters
• 60 lb bag: about 0.45 cubic feet, or about 0.013 cubic meters
• 40 lb bag: about 0.3 cubic feet, or about 0.008 cubic meters

Example. A 2 cubic meter pour, using 80 lb bags at 0.017 m³ each:

2 ÷ 0.017 ≈ 117.6, rounded up to 118 bags

Always round the bag count up, since a partial bag still needs to be bought in full.

Concrete volume for a circular slab

A round slab, such as a footing for a post or a circular patio, uses a different formula:

Volume = π × radius² × depth

Find the radius (half the diameter), square it, multiply by π (about 3.14159), then multiply by the depth. For any shape that is not a simple rectangle or circle, split it into smaller rectangular or circular sections, find the volume of each, and add them together.

Frequently asked questions

What is the formula for calculating concrete volume? Volume equals length times width times depth, with all three measurements in the same unit. For a circular slab, volume equals π times the radius squared times the depth.

Should concrete volume be rounded up? Yes. Rounding up, and adding a 5–10% waste allowance, avoids running short of concrete partway through a pour, which can weaken the finished slab at the seam.

How many bags of concrete do I need for a small job? Divide the total volume by the coverage of one bag. An 80 lb bag covers about 0.017 cubic meters (0.6 cubic feet), so a 1 cubic meter pour needs about 59 bags before rounding up for waste.

What is the standard depth for a driveway or patio? Driveways are usually 10–15 cm (4–6 inches) thick. Patios and sidewalks are usually 10 cm (4 inches) thick. Foundation slabs are usually 15–20 cm (6–8 inches) thick, and can be thicker under heavy loads.

How do cubic meters and cubic yards compare? One cubic meter equals about 1.31 cubic yards. One cubic yard equals about 0.765 cubic meters. Metric countries order concrete by the cubic meter; the United States orders it by the cubic yard.

How is concrete volume calculated for an irregular area? Split the area into rectangles or circles, calculate the volume of each section separately, then add the results together for the total volume needed.