Concrete Quantity Calculator
Work out the concrete volume needed for a slab or foundation, with a waste allowance, plus its weight and delivered cost.
💼 Are you a real estate agent or broker? Send this calculator to your buyers on your own branded listing page — every enquiry comes straight to your WhatsApp. Create free agent page →Concrete is ordered by volume and delivered in fixed loads, so ordering slightly short means a second delivery charge for a small quantity — usually far more expensive than the extra material would have been.
The volume itself is simple geometry. What catches people out is the waste allowance for uneven ground, over-dig and spillage, which on a domestic slab is commonly five to ten percent.
The calculation
Volume = length × width × thickness, all in the same units. Add the waste allowance to get the quantity to order, and multiply by the density for an approximate weight, which matters for access and delivery planning.
Worked example
A slab 8 by 5 at 0.15 thick is 6 cubic metres net. With a 5% waste allowance you order 6.3, costing 819 at 130 per cubic metre and weighing about 15,120 kilograms — over fifteen tonnes, which is what determines whether the delivery vehicle can reach the pour.
Order once, generously
A short load charge for a small top-up frequently costs more than a whole extra cubic metre would have. Where the ground is uneven or the excavation over-dug, ten percent is a safer allowance than five.
Turn a calculation into an enquiry
Buyers who run these numbers are ready to talk. Give every listing its own page with your photo, phone and WhatsApp on it — leads land straight on your phone.
Create your free property pageFrequently asked questions
How much waste should I allow?
Five percent on a well-prepared level base and up to ten where the ground is uneven or the excavation over-dug. Trench fill in soft ground can need considerably more, since the concrete follows the shape of the dig.
Does the weight matter?
Yes, for access. Concrete is roughly 2.4 tonnes per cubic metre, so a modest slab is a heavy delivery. Check that the vehicle can reach the pour, or budget for a pump, which is a substantial extra cost.
Should I mix on site instead?
Only for very small quantities. Beyond about half a cubic metre, ready-mixed is cheaper, more consistent and vastly faster, and consistency matters structurally in a way that hand mixing struggles to achieve.