Calculate the amount of concrete required for slabs, foundations, footings, pads and other rectangular projects. Enter your dimensions, choose Metric or Imperial units, add a waste allowance, and get the required volume in cubic metres, cubic yards and cubic feet.
Enter the length, width and depth of your concrete area.
Base volume: 0 m3
Waste allowance: 0 m3
Planning volume: 0 m3
How to Calculate Concrete Volume
Concrete volume is calculated by multiplying length by width by depth. The three measurements must use the same unit before multiplication.
For a rectangular slab, measure the full length and width of the area, then enter the slab thickness as the depth. The calculator converts the measurements to metres before calculating the volume.
Example: Concrete for a 20 ft × 10 ft Slab
Length: 20 ft
Width: 10 ft
Depth: 4 in
Convert the 4-inch depth to feet: 4 ÷ 12 = 0.3333 ft
Volume: 20 × 10 × 0.3333 = 66.67 ft3
This equals approximately 1.887 m3 or 2.469 yd3.
With a 10% waste allowance, the planning quantity becomes approximately 2.075 m3 or 2.716 yd3.
What Does the Waste Allowance Cover?
The waste allowance accounts for small measurement differences, uneven surfaces, spillage, handling losses and minor variations during placement. It does not replace accurate site measurements.
A simple rectangular slab on a prepared surface often needs less allowance than a project with irregular forms, difficult access or uneven excavation.
Metric and Imperial Concrete Measurements
BuildMetric supports both measurement systems because construction projects use different regional standards. Metric measurements are converted to metres before the volume calculation. Imperial measurements are converted to feet before calculation.
The calculator reports the result in cubic metres, cubic yards and cubic feet so you can compare the quantity with supplier quotations or project specifications.
Common Concrete Calculation Mistakes
- Entering slab thickness in inches while treating it as feet.
- Mixing metres and centimetres without converting the measurements.
- Using the wrong depth for a sloped or stepped area.
- Ignoring changes in slab thickness across the project.
- Ordering the exact calculated volume without allowing for reasonable site losses.
Concrete Calculator FAQs
How much concrete do I need for a slab?
Multiply the slab length by its width and thickness. The result gives the basic concrete volume. Add an appropriate waste allowance for planning and ordering.
How do I calculate concrete in cubic yards?
Calculate the volume first, then convert the result to cubic yards. One cubic metre equals approximately 1.308 cubic yards.
How much waste should I add to concrete?
A 5% to 10% allowance is often used for straightforward rectangular work. More complicated projects might need a different allowance based on site conditions.
Does this calculator calculate concrete bags?
No. Concrete bag yields vary by product, bag size and mix. Use the calculated volume with the yield printed on the specific product packaging for a bag estimate.
Can I use this calculator for footings?
Yes, when the footing has a rectangular shape with a consistent width and depth. Stepped, tapered or irregular footings should be divided into separate sections and calculated individually.