What does the mix ratio 1:2:4 mean?

The numbers represent parts by volume: 1 part cement, 2 parts sand (fine aggregate), and 4 parts coarse aggregate. The higher the cement proportion, the stronger the mix. 1:2:4 is a nominal M15 mix (characteristic strength ~15 MPa); 1:1.5:3 is M20 (~20 MPa).

Why is a dry volume factor of 1.30 used?

Dry ingredients occupy more volume than the same ingredients in a wet mix due to voids between particles. Multiplying the wet volume by 1.30 (a standard industry value) accounts for this compaction and gives you the correct dry quantities to measure out.

How many 50 kg bags of cement per cubic meter of M20 concrete?

For a 1:1.5:3 (M20) mix with a 1.30 dry-volume factor, you need roughly 8.2 bags of 50 kg cement per cubic meter of finished concrete. This calculator gives the exact figure for your chosen volume and mix.

Does this include a waste allowance?

The 30% dry-volume factor already accounts for typical compaction losses. For jobs with significant wastage (uneven sub-base, complex formwork), add a further 5–10% on top when ordering materials.

Can I use a custom ratio not in the preset list?

Yes. Select "Custom" from the mix grade dropdown and enter any cement:sand:aggregate ratio directly — for example 1:3:6 for lean concrete blinding or 1:1:2 for high-strength work.

Concrete Mix Ratio Calculator

Name: Concrete Mix Ratio Calculator
Availability: InStock
Author: Nham Vu

Enter your mix ratio (e.g. 1:2:4) and target volume to get the exact weight of cement, sand, and aggregate — plus bag count — with a 30% dry volume factor applied.

Mix Parameters

Mix Grade / Ratio

Target Volume

Advanced options

Dry Volume Factor

Standard: 1.30. Use 1.54 for volume-batching methods.

Cement Density (kg/m³)

Sand Density (kg/m³)

Aggregate Density (kg/m³)

Cement Bag Weight (kg)

Set your mix parameters and click Calculate.

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Summary

Enter your mix ratio (e.g. 1:2:4) and target volume to get the exact weight of cement, sand, and aggregate — plus bag count — with a 30% dry volume factor applied.

How it works

Select a standard mix grade (M10 through M25) or enter a custom cement:sand:aggregate ratio.
Choose your target concrete volume and unit (cubic meters or cubic feet).
Optionally adjust the dry volume factor (default 1.30) and cement density (default 1440 kg/m³).
Click Calculate to see ingredient quantities broken down by weight and volume.
Cement result includes bag count based on standard 50 kg bags.
All results include a summary you can copy for ordering or job-site reference.

Use cases

Estimating cement bags and aggregate for a foundation or column pour.
Cross-checking a ready-mix order against a hand-mixed batch calculation.
Comparing material costs between M15 (1:2:4) and M20 (1:1.5:3) mixes.
Planning material quantities before a rural or off-grid construction project.
Verifying a contractor's material estimate for footings or slab work.
Teaching concrete proportioning in civil engineering coursework.
Converting between cubic-meter and cubic-foot volume inputs on site.

Frequently Asked Questions

Last updated: 2026-06-10 · Reviewed by Nham Vu