Concrete Calculator
About the Concrete Calculator
Estimate the volume of concrete for a slab, footing, or column and how much cement, sand, and coarse aggregate you need for a chosen mix grade. Enter the dimensions, pick a mix, and get material quantities you can order. Enter your dimensions, choose a mix grade and check the quantities before you place an order.
This tool works in your browser: the files and text you use are processed on your device and are not uploaded.
How to use it
- Enter the length, width, and thickness (depth) of the pour.
- Choose a concrete grade / mix ratio (e.g. M15 = 1:2:4).
- Read the volume plus the cement bags, sand, and aggregate.
Frequently asked questions
How much cement, sand, and aggregate are in a mix?
The material split follows the mix ratio. For M15 (1:2:4) the parts total 7, so cement is 1/7, sand 2/7, and aggregate 4/7 of the dry volume. Dry volume is taken as about 1.54× the wet (finished) concrete volume.
How many bags of cement per cubic metre?
It depends on the grade. Roughly, M15 needs about 6.3 bags/m³, M20 about 8 bags/m³, and M25 about 9.5 bags/m³ of concrete. The calculator works this out from your exact volume and mix.
What do M15, M20, and M25 mean?
The M number is the concrete’s characteristic compressive strength in N/mm² (MPa) at 28 days. Higher grades use more cement (a richer mix) and are used for more heavily loaded structural elements.
Why is dry volume more than the finished volume?
Dry cement, sand, and aggregate contain voids and bulk up; when mixed with water they consolidate. Multiplying the wet volume by ~1.54 accounts for this so you buy enough dry material.