Free calculator
Concrete Calculator
Work out concrete volume, bags, and cost for a slab, footing, or column, metric or imperial, with a standard 5% waste allowance. Free, no sign-up.
Volume includes a standard 5% waste allowance. Bag yields are typical for pre-mixed concrete; check your supplier's stated yield. For a full set of quantities off a real plan, take off concrete areas to scale in the app.
Estimating a whole job? Calibrate the plan once and take off quantities straight off the drawing with ContractorCounter's concrete takeoff software so they flow into a live bill of quantities and a quote.
How to calculate concrete
For a slab or footing, concrete volume is length × width × thickness, with every dimension in the same unit. For a round column it is π × (diameter ÷ 2)² × height. Convert the result to cubic metres or cubic yards (1 yd³ ≈ 0.765 m³), then add a waste allowance (this calculator uses 5%) before you order.
To get the number of pre-mixed bags, divide the total volume by the yield of one bag. A 20 kg bag yields roughly 0.009 m³, so a 0.2 m³ pour needs about 23 bags. For anything beyond a small pour, ordering ready-mix by the cubic metre is usually cheaper than bags.
FAQ
How do you calculate concrete volume?
Multiply length × width × thickness for a slab or footing (all in the same unit) to get volume, then convert to cubic metres or cubic yards. For a round column, use π × (diameter ÷ 2)² × height. This calculator does it for you and adds a standard 5% waste allowance.
How many bags of concrete do I need?
Divide the total concrete volume by the yield of one bag. Typical pre-mix yields are about 0.009 m³ for a 20 kg bag, 0.0115 m³ for 25 kg, and 0.0138 m³ for 30 kg, but always check your supplier's stated yield. The calculator rounds up to whole bags.
How much concrete is in a cubic yard vs a cubic metre?
One cubic yard equals about 0.765 cubic metres, so one cubic metre is about 1.31 cubic yards. The calculator shows both so you can order in whichever unit your supplier uses.
Why add a waste allowance?
Spillage, over-excavation, uneven subgrade, and form deflection mean you almost always pour slightly more than the theoretical volume. A 5% allowance is a common rule of thumb; increase it for rough ground or complex pours.