1001 Pro Calculators and Tools · Home & construction
Concrete calculator: how many bags
Put in the volume you need to fill and the bag you are buying. It tells you how many bags to buy, rounded up, with a waste allowance on top.
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A 25 kg bag of premixed concrete makes about 0.0125 m³ once mixed, so a cubic metre takes about 80 bags. The waste allowance covers spillage, an uneven base and what is left in the mixer; 5 to 10% is usual.
Past about 30 bags, ready-mix delivered by the cubic metre is usually cheaper and far less work.
In the app
- Work out the volume from a slab's, footing's or post hole's measurements
- Add it to a job with your other materials and send the customer a PDF quote
- Mortar, bricks, blocks, plasterboard, tiles and paint for the rest of the job
- The step-by-step working behind every answer
Questions people ask
How many 25 kg bags of concrete make a cubic metre?
About 80. A 25 kg bag yields roughly 0.0125 m³ of concrete, so 1 m³ needs 80 bags before any allowance for waste.
How much waste should I allow for concrete?
Around 5% for a neat job on a firm, level base, and 10% where the ground is uneven or the shape is awkward.