Estimates for planning and ordering. Every assumption can be changed.
Concrete calculator
Enter the size of your slab, base or footing to see the volume in cubic metres and roughly how many bags of mix you need.
How this is worked out
Volume is length times width times depth, plus an allowance for waste and uneven ground. The bag count uses the concrete weight shown in the assumptions, which you can change. Bagged mixes differ, so check the yield printed on the bag. For more than about one cubic metre, ready-mixed concrete delivered by lorry is usually easier.
Common questions
How thick should a shed base be?
Many shed bases are 75mm to 100mm of concrete on a compacted sub-base, but follow the shed maker's instructions.
How many 25kg bags make a cubic metre?
At 2,400kg per cubic metre, 96 bags. The real figure depends on the product, so check the bag.
These are estimates for planning and ordering. Materials, bag sizes and densities vary by product, so always check the figures on the packaging or with your supplier before you order. For structural work, follow the advice of a qualified builder or engineer.