Concrete calculator
Concrete calculator. Cubic metres, bags and a rough cost.
Work out how much concrete you need for a slab, path, footing or post holes, in cubic metres and in bags of premix. Add an allowance for spillage and uneven ground, and your price per cubic metre for a rough cost.
- Free, no sign-up
- Works on your phone
- Nothing leaves your browser
- Allowance and rough cost
You need about
–
A rough guide only. Measurements, ground conditions and supplier yields vary; confirm quantities before you order.
For tradies
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With your rates, your name and your phone number. Every result ends with “Get an exact quote”, and the enquiry reaches you with the measurements already filled in, so you can quote without ringing back to ask.
- Included on every Raptor Sites plan, from $20 a month.
How the numbers are worked out
- Slabs, paths and footings
- Length × width × depth. Enter the depth in millimetres, as shown on your plans or set by your engineer.
- Post holes and piers
- π × radius² × depth for each hole, times the number of holes.
- Bags of premix
- The volume divided by what one bag makes, rounded up to whole bags. Bag yields are the manufacturers’ own figures.
- The allowance
- An extra percentage for spillage, uneven ground and over-dig. It starts at 5%, as Cement Australia’s and Dingo’s calculators do; set it to suit the job.
Bag yields, from the manufacturers (checked 29 October 2026):
- Cement Australia, FAQs: "Approximately 110 x 20kg Concrete Mix bags are required."
- Boral, Concrete Mix product data sheet: "108 x 20kg bags equates to one cubic metre of mixed concrete."
- Easy Mix, Concrete technical data sheet: "100 x 20kg Bags = 1.0m3"
- Easy Mix, Rapid Set Concrete technical data sheet: "67 x 30kg Bags = 1.0m3"
- Cement Australia, slab calculator: "There is a 5% allowance for wastage included in this calculation."
Questions
Asked before starting. Answered plainly.
How many bags of concrete do I need?
Enter your slab or holes, pick the bag you are buying and the calculator divides the volume by that bag’s yield, rounding up. For bigger jobs, premixed concrete by the cubic metre is usually easier than bags.
How much does concrete cost per cubic metre?
It varies with your area, the mix, the amount and delivery. Enter the price per cubic metre from your supplier’s quote and the calculator multiplies it out for a rough figure.
How much extra concrete should I allow?
Cement Australia’s and Dingo’s own slab calculators add 5% for wastage, so this one starts at 5%. Raise it for uneven ground, over-dug holes or a long barrow run.
How thick should a slab be?
It depends on what the slab is for and the ground underneath. Follow your plans, engineer or local council; the calculator just works out the volume for the depth you enter.
Is it free?
Yes. No sign-up, and nothing you enter leaves your browser.
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