Concrete Volume Calculator for Slabs and Footings: Cubic Metres, Truck Loads and Reinforcement
Work out how much concrete to order for a slab or footing.
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Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.
How this calculator works
Enter the length, width and thickness, the number of identical slabs, the allowance for waste and the truck size.
The calculator finds the volume, adds the allowance, and gives the number of truck loads, the weight, the area to be finished and the length of edge formwork.
With a reinforcing rate in kilograms per cubic metre it gives the steel, and with a price it gives the cost.
Formulas used
- V = L\,W\,t\,n
- V_o = V(1 + w)
- m = 2400\,V
- m_s = V\times\text{rate}
Worked example
With the default numbers in the calculator above:
- Volume of concrete in the finished work: 8.00 m3
- Volume to order, with the allowance for waste: 8.40 m3
- Number of truck loads: 1.40 loads; order 2 trucks or 8.40 m3 (a short load fee often applies below about 3 m3)
- Weight of the concrete (2400 kg/m3): 19.20 tonnes
- Area of the top surface to be finished: 80.00 m2
- Length of edge formwork around the slabs: 36.00 m
- Reinforcing steel: 400.00 kg (0.40 tonnes)
Change the numbers in the calculator to see the full working, every step, for your own case.
Common questions
How much extra concrete should I order?
About 5 to 10 percent, to allow for uneven ground, spills and the pump.
What does concrete weigh?
About 2400 kg per cubic metre, and 2500 for reinforced concrete.
How thick should a slab be?
It depends on the load. A path is 75 to 100 mm, a house slab 100 mm with thickenings, and a driveway 100 to 150 mm. Check AS 2870 and AS 3600.
Is the reinforcement figure exact?
No. It is a rough rate. The real quantity is taken off the structural drawings.
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Got a question about this? Ask an engineering question and get a plain-language answer with references.
Further reading: AS 3600 Concrete structures; AS 2870 Residential slabs and footings; AS 1379 Specification and supply of concrete.
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