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Concrete Mix Calculator

Work out cement, sand, gravel and water for a concrete pour from a volumetric mix ratio. Enter the volume and ratio, then press Calculate.

Written and reviewed by SM Arijul Islam · Last reviewed 29 October 2026 · Editorial standards · Report an error

About the Concrete Mix Calculator

A 1:2:3 concrete mix means one part cement, two parts sand and three parts gravel by volume. Dry ingredients bulk up when mixed with water, so the total dry volume is about 1.54 times the finished wet volume. For 1 m³ of concrete you therefore need about 1.54 m³ of dry material, split in the ratio 1:2:3.

This is a nominal mix for general work, not a structural design. Strength depends on the water-cement ratio, aggregate grading, compaction and curing. A 0.5 water-cement ratio is a common starting point; adding water to make the mix easier to place weakens it.

How the calculation works

Dry volume = wet volume × 1.54.
Cement volume = dry volume × cement parts ÷ total parts.
Mass = volume × bulk density (cement 1,440; sand 1,600; gravel 1,500 kg/m³).
Water (L) = cement mass × water-cement ratio.

Reference values

Nominal concrete mixes
Mix	Cement (bags/m³)	Typical use
1:3:6	4.4	Mass fill, blinding
1:2:4	6.0	General internal slabs
1:2:3	7.0	General reinforced work
1:1.5:3	8.0	Higher-strength slabs
1:1:2	9.5	Thin sections, high strength

Worked example: two cubic metres of 1:2:3

For 2 m³ of 1:2:3 concrete, the dry volume is 2 × 1.54 = 3.08 m³. Cement is 3.08 × 1/6 = 0.513 m³, about 739 kg or 14.8 bags of 50 kg. Sand is 1.027 m³ (about 1,643 kg) and gravel 1.540 m³ (about 2,310 kg). At a 0.5 water-cement ratio, water is about 370 L.

Those quantities assume reasonable aggregate grading and no site waste. Order 5–10% extra for spillage, uneven subgrade and over-excavation. Adding water beyond the specified ratio makes the mix easier to place but lowers strength, so adjust the aggregate or use a plasticiser instead.

Slump, curing and strength

Strength depends on the water-cement ratio more than on the mix proportions. Adding water to make placing easier raises the ratio and lowers the final strength, roughly 5% for every extra 0.01 in the ratio. A plasticiser improves workability without that penalty, which is why it is preferred on site over a splash of extra water.

Curing matters as much as mixing. Concrete gains strength while moisture is present, so it should be kept damp for several days after placing, especially in hot or windy weather. Drying out early can leave a surface that dusts or cracks even though the mix itself was correct. Formwork should stay in place until the concrete can carry the loads it was designed for.

Frequently asked questions

How many 50 kg bags are in a cubic metre?

A 1:2:3 mix needs about 7 bags of cement per m³, depending on the exact bulk density and waste. This calculator uses 1,440 kg/m³ for cement.

Can I add more water to make it workable?

Adding water raises the water-cement ratio and lowers strength. Use a plasticiser or adjust the aggregate grading instead.

Is this a structural design?

No. It is a quantity estimate for nominal mixes. Structural concrete needs a specified mix design and testing.

Can I add more water to make the mix workable?

Only within the specified water-cement ratio. Extra water increases workability but lowers strength and durability. Use a plasticiser or adjust the aggregate grading instead.

Sources and standards

Mix proportions here start from the volumetric and weight ratios in ACI 211.1, then convert between them using the densities stated in the table. Cement, aggregate and water densities vary by source, so a batch weight is an estimate until it is checked against the supplier's data.