Concrete bag calculator (premix bags)
Made for small home jobs where you mix bags by hand instead of ordering ready-mixed concrete from a plant.
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How to use it
- Enter length, width, depth, yield per bag and waste allowance.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Volume in litres = length × width × (depth ÷ 100) × 1000. Bags = volume × (1 + waste ÷ 100) ÷ bag yield in litres, rounded up.
Example
Inputs: Length = 2 m, Width = 1 m, Depth = 10 cm, Yield per bag = 17 L, Waste allowance = 5 %. Result: Bags needed: 13 bags; Concrete volume: 0.2 m³; Volume in litres: 200 L.
Limits and caveats
- Bag yield differs between makers, so copy the figure printed on your bag.
- Above roughly 1 m³, ordering ready-mixed concrete is usually more practical.
Questions about this tool
What yield should I use?
Read it on the bag. An 80 lb US bag makes about 0.6 ft³, close to 17 litres, and smaller bags make less.
How many bags for a 1 × 1 m pad 10 cm deep?
That is 100 litres, so with a 17 litre yield you need 6 bags before waste (5.88 rounded up).
Why is the count always rounded up?
You cannot buy part of a bag, and running short mid-pour leaves a weak joint in the concrete.