How Many Bags of Concrete per Cubic Meter

Reference

The question every weekend pour starts with. The honest answer is printed on the bag, but the standard yields land close enough together that good planning numbers exist.

25 kg bag: about 85 per cubic meter. 30 kg: about 71. 80 lb: about 59.
20 kg bag, yield about 9.5 Labout 106 bags per m3
25 kg bag, yield about 12 Labout 85 bags per m3
30 kg bag, yield about 14 Labout 71 bags per m3
40 lb bag, yield 0.30 cu ftabout 118 per m3, 90 per cubic yard
60 lb bag, yield 0.45 cu ftabout 79 per m3, 60 per cubic yard
80 lb bag, yield 0.60 cu ftabout 59 per m3, 45 per cubic yard
The formulabags = volume needed divided by yield, rounded up

Notes for design and site

Where the numbers come from: placed concrete runs about 2350 kg/m3, and a bag yields its own mass plus mixing water divided by that density. Run a 25 kg bag through it and you get 11.8 L, which matches the printed yields almost exactly. Yields do vary a little by product, so when the bag says something different, the bag wins.

Scale is the real lesson. A post footing of 0.1 m3 is eight or nine 25 kg bags, a pleasant morning. A full cubic meter is 85 bags, over two tonnes of material through a wheelbarrow mixer one batch at a time. Past about half a cube, ready mix beats bags on cost, consistency and your back. Whatever the size, add 5 to 10 percent for waste and spillage.

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