What is the Concrete Calculator?
Planning a roof slab, floor, column or footing? This concrete calculator works out the volume of concrete and the materials you need: 50 kg cement bags, sand and crush (gravel), for common nominal mixes like 1:2:4 (M15), 1:1.5:3 (M20) and 1:3:6 (M10).
It supports feet/inches and metres/centimetres and includes a wastage allowance, so you can order the right amount and avoid extra trips to the supplier.
How to use the Concrete Calculator
- Choose the shape and units.
- Enter length, width and thickness (and quantity).
- Pick the mix ratio and read the materials needed.
How it is calculated
Wet volume × 1.54 = dry volume. Each material is its share of the mix ratio. Cement volume × 1440 kg/m³ ÷ 50 = number of bags. Example: a 20 × 15 ft slab, 5 inches thick, 1:2:4 mix needs about 3.7 m³ of concrete and around 24 bags of cement (with 5% wastage).
Frequently asked questions
What mix is used for a house roof slab?
1:2:4 (M15) or 1:1.5:3 (M20) are common – follow your structural engineer’s drawings.
How thick should a roof slab be?
Usually 4.5–6 inches for houses, depending on span.
Does it include steel?
No, reinforcement steel is calculated separately.
Is it exact?
It is a good estimate; site conditions and wastage vary.
This concrete calculator is 100% free, needs no signup and works on phones, tablets and computers. Your data is processed in your browser and never uploaded.
Last updated: · By NodifyTech