HOW MUCH CONCRETE DO YOU NEED?
Enter your job dimensions, pick a grade, get your spec in seconds. Procon mixes on-site — pay only for what you actually pour.
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How to calculate how much concrete you need
Concrete is ordered in cubic metres. Measure the pour in metres, multiply the dimensions together, then add about 10% for wastage. That is the whole method, and it is the same arithmetic any supplier runs on your behalf.
Slab or base
length × width × depth
A 4 m × 3 m base at 100 mm: 4 × 3 × 0.1 = 1.2 m³
Strip footing
length × width × depth
A 10 m run, 0.6 m wide, 0.3 m deep: 10 × 0.6 × 0.3 = 1.8 m³
Column or pad
π × (diameter ÷ 2)² × height
A 0.3 m column, 1 m high: 3.14 × 0.15² × 1 = 0.07 m³
Steps
width × riser × tread × (n(n+1) ÷ 2)
3 steps, 1 m wide, 170 mm rise, 280 mm tread = 0.29 m³
Converting millimetres to metres
Depth is usually specified in millimetres and volume is calculated in metres, which is where most ordering mistakes start. Divide by 1000: 100 mm is 0.1 m, 150 mm is 0.15 m, and 300 mm is 0.3 m. Getting this wrong by one decimal place orders ten times the concrete you need.
What 1 m³ actually covers
One cubic metre covers 10 m² at 100 mm deep, 6.7 m² at 150 mm, or 5 m² at 200 mm. It weighs roughly 2.3 to 2.4 tonnes. For a sense of cost per metre by grade, see our concrete price per m³ guide, and if you are weighing bagged mix against a delivery, the bagged ready-mix guide covers the break-even point.
Concrete calculator questions
- How do I calculate how much concrete I need?
- Multiply length by width by depth, all in metres, to get cubic metres. A 4 m by 3 m slab at 100 mm deep is 4 × 3 × 0.1 = 1.2 m³. Add around 10% for wastage, spillage and uneven sub-base. The calculator on this page does both steps for you and gives you the grade as well as the volume.
- How much concrete is in 1 cubic metre?
- One cubic metre of concrete fills a space one metre long, one metre wide and one metre deep. It weighs roughly 2.3 to 2.4 tonnes depending on the mix, and covers 10 m² at 100 mm deep or 6.7 m² at 150 mm deep.
- How much extra concrete should I order for wastage?
- Ten per cent is the standard allowance for spillage, an uneven sub-base and slight over-dig. With volumetric concrete this matters far less than with drum-mixed deliveries, because the mix happens on site and you pay only for what you actually discharge, so there is no cost in over-estimating slightly.
- What concrete grade do I need?
- C25/30 suits domestic floors, shed bases and light footings. C30/37 covers driveways, paths and most foundations. C32/40 and above is for structural slabs, beams and columns. If you are unsure, pick the closest match in the calculator or call the team, because specifying too low is far more expensive to fix than specifying slightly high.
- Is the concrete calculator accurate enough to order from?
- It is accurate for ordering, and it is the same arithmetic a supplier uses. It cannot see your site, so it does not know about an uneven sub-base, over-dig, or formwork that has moved. Treat the figure as your order quantity, keep the 10% wastage allowance on, and with volumetric supply any surplus simply is not discharged or charged for.
- Do I pay for concrete I do not use?
- Not with volumetric concrete. The mixer batches on site, so you are charged for the volume actually discharged rather than a pre-mixed drum load. That is the main reason an over-estimate carries no penalty with Procon, and why part-load charges do not apply.
Get a volumetric concrete price in 30 minutes
Volumetric concrete. Mixed on your site. Pay for what you pour.
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