Concrete calculators
Bags of concrete for slabs, footings and fence posts.
Before you buy
Bagged concrete is sold differently around the world: 40, 50, 60 and 80 lb bags in the US, 20 kg bags in the UK and Australia, and 30 kg bags in Canada. Each size gives a different volume of finished concrete, so the bag count depends on what your local store sells.
Our concrete calculators use yields published by manufacturers and retailers. They let you type the figure from your own bag if it's different.
Quick tips
- Measure inside the forms or the hole. That's the space you need to fill.
- Keep about 10% extra for uneven ground and spills.
- For fence posts, a wider hole uses a lot more concrete. Check the hole size before you buy.
- For large slabs, compare the cost of many bags with a ready-mix delivery.
Every calculator shows its formula and sources. See how we calculate.