What is the 1:2:4 concrete mix ratio?

A 1:2:4 mix ratio means 1 part cement : 2 parts sand : 4 parts aggregate (coarse) by volume. It is a common general-purpose mix equivalent to M15 grade (15 MPa compressive strength). It is used for non-structural work such as footpaths, garden paths, floor slabs, and minor foundations.

How do I calculate how many bags of cement I need?

First calculate the dry volume of concrete needed = wet volume × 1.54 (a 54% factor accounts for compaction and void filling when dry ingredients are mixed with water). Then find the cement portion: cement volume = (C / total parts) × dry volume. Convert to weight: cement weight = volume × 1440 kg/m³ (bulk density). Divide by 50 kg (standard bag size) to get the number of bags.

What is the dry volume factor of 1.54?

When you mix dry cement, sand, and aggregate, the wet concrete volume is less than the sum of dry ingredient volumes because smaller particles fill the voids between larger ones. The factor 1.54 accounts for this — to produce 1 m³ of wet concrete, you need about 1.54 m³ of dry ingredients. This is an industry-standard estimate; values between 1.50 and 1.57 are used in practice.

What mix ratio should I use for structural concrete?

For structural elements (beams, columns, slabs carrying loads): use M20 grade (1:1.5:3) for general structural work, or M25 (1:1:2) for higher loads. Never use M15 (1:2:4) for structural elements. For very heavy or exposed structures, consult an engineer — mix designs above M30 typically require a laboratory mix design rather than a nominal ratio.

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Concrete Mix Calculator

Calculate cement bags, sand, and aggregate quantities for any concrete volume and mix ratio. Supports M15 (1:2:4), M20 (1:1.5:3), M25 (1:1:2), M10 (1:3:6), and custom ratios.

Concrete Volume

Input Mode

Volume (m³)

1 m³ = 1,000 litres. A standard slab 4m × 3m × 0.1m thick = 1.2 m³.

Mix Ratio (Cement : Sand : Aggregate)

Options

Cement Bag Size (kg)

Wastage Factor (%)

Dry Volume Factor

Material Quantities

Wet Volume

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m³

Dry Volume

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m³

With Wastage

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m³ dry

Cement

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bags needed

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Sand (Fine Aggregate)

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kg needed

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Aggregate (Coarse)

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kg needed

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Mix Proportion by Volume

Cement — Sand — Aggregate —

Concrete Grade Reference

Grade	Mix Ratio (C:S:A)	Strength (MPa)	Use Case
M5	1:5:10	5	Lean concrete, blinding
M7.5	1:4:8	7.5	Plain concrete footings
M10	1:3:6	10	Mass concrete, non-structural fill
M15	1:2:4	15	Footpaths, floor slabs, kerbs
M20	1:1.5:3	20	Structural: slabs, beams, columns
M25	1:1:2	25	Heavy structural, water-retaining
M30+	Design mix	30+	High-rise, bridges, industrial

Bold rows are most commonly used in residential and light commercial construction.

Frequently Asked Questions

A 1:2:4 mix means 1 part cement : 2 parts sand : 4 parts coarse aggregate by volume. This is M15 grade concrete (15 MPa characteristic compressive strength). It is used for general non-structural work: footpaths, garden paths, blinding layers, minor floor slabs. For structural elements like beams, columns, or load-bearing slabs, use M20 (1:1.5:3) or higher.

It depends on the mix ratio. For M15 (1:2:4): approximately 6–7 bags of 50 kg cement per m³ of concrete. For M20 (1:1.5:3): approximately 8–9 bags. For M25 (1:1:2): approximately 11–12 bags. Use this calculator for your exact volume and ratio.

Dry concrete ingredients, when mixed together, compact and fill each other's voids. The resulting wet concrete volume is smaller than the dry ingredient volume. To produce 1 m³ of wet concrete you need 1.54 m³ of dry ingredients (or 1.50–1.57 depending on aggregate type). This calculator applies the factor before computing ingredient quantities.

For structural elements (beams, columns, slabs with loads): minimum M20 (1:1.5:3). For water-retaining structures, exposed environments, or critical loads: M25 (1:1:2) or higher. Above M30, use a laboratory-designed mix — nominal ratios become unreliable at high strengths. Always consult a structural engineer for load-bearing design.

How to Calculate Concrete Mix Quantities

The process follows three steps: (1) Find the wet volume of concrete needed. (2) Multiply by the dry volume factor (1.54) and wastage factor to get total dry ingredient volume. (3) Split the dry volume proportionally between cement, sand, and aggregate based on the mix ratio, then convert to weights using bulk densities.

Bulk Densities Used in This Calculator

Cement: 1,440 kg/m³ (bulk density of Portland cement)
Sand (fine aggregate): 1,600 kg/m³
Coarse aggregate: 1,500 kg/m³

Water-to-Cement Ratio

This calculator does not include water volume because the water requirement depends on the desired workability (slump), ambient temperature, and whether admixtures are used. As a rough guide, the water-to-cement (w/c) ratio for nominal mixes is typically 0.45–0.55 by weight. Lower w/c ratios produce stronger concrete; higher ratios make it easier to place but weaker. Never add extra water to make concrete easier to pour — use plasticisers instead.