Concrete Calculator

Estimate cement, sand, and aggregate for a nominal concrete mix from a slab size or a volume.

Enter the values and press Calculate.

Your result will show here.

About this calculator

A nominal concrete mix splits cement, sand, and aggregate in a fixed ratio such as 1:1.5:3 for M20. The wet volume of the slab or the footing is increased by 1.54 to estimate the dry materials. Each material then takes its share of that dry volume.

Enter the size in metres or feet. Thickness is easy to mistype: 125 mm is 0.125 metres, not 125 metres. If you already have the wet volume from a drawing, use the volume mode and skip the dimensions.

Higher grades on an important structure should follow a design mix, not a nominal ratio copied from a general page. This calculator is for planning quantities and for checking an order of magnitude.

Water is left out on purpose. A guessed water quantity causes more harm than an omitted line. Follow the engineer or the plant.

Nominal mix quantities

Wet volume = length × width × thickness, or the volume you enter
Dry volume = wet volume × 1.54
Each material = dry volume × its parts / total parts
Cement bags = cement volume × 1,440 / 50

Nominal ratios used here:
M5 1:5:10, M7.5 1:4:8, M10 1:3:6, M15 1:2:4, M20 1:1.5:3, M25 1:1:2

Example: 1 cubic metre of M20

One cubic metre of wet M20 concrete, nominal ratio 1:1.5:3, dry factor 1.54.

Cement is 8.06 bags. Sand and aggregate are on the result card in cubic metres.

Order whole bags. Do not invent a water quantity from this page.

1 m³ nominal M20

Ratio 1 : 1.5 : 3, dry factor 1.54.

8.06 bags

How to use

Choose a slab size or a volume you already know.
For a slab, enter length, width, and thickness in metres or feet.
Choose the nominal grade.
Press Calculate.
Ask the engineer before you treat M20 or M25 as a designed mix.

Important notes

These are nominal ratios for planning, not a laboratory mix design.
Water is intentionally omitted. The water-cement ratio belongs to the mix design or the batching plant.
The dry factor 1.54 is a common concrete allowance. Your specification may differ.
Reinforcement steel is not included.

FAQ

What is nominal M20?

The ratio used here is 1 : 1.5 : 3 of cement, sand, and aggregate. A designed mix for the same grade can differ.

Why is there no water line?

The water-cement ratio is part of the mix design. Guessing it from a volume calculator is a bad idea, so this page does not do it.

What is the 1.54 factor?

Dry materials occupy more volume than the wet concrete they produce. 1.54 is the factor used in this estimate.

Does this include steel?

No. It is only cement, sand, and aggregate for the wet volume you enter.

Disclaimer

Results are estimates for general information. Verify important decisions with an appropriate professional or official source. Structural concrete needs the grade and mix specified for the job.

Last updated 5 October 2026.

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