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Cement Bags Calculator

Cement bags, sand and aggregate for a given volume and grade. The familiar figure of about eight bags per cubic metre for M20 falls straight out of the arithmetic rather than being quoted.

Also called: cement quantity calculator, bags of cement per m3.

Cement bags
24.19

24.19 bags for 3 m³ of M20, which is 1,209.6 kg of cement. Sand comes to 1.26 m³ and aggregate to 2.52 m³.

Cement (kg)
1,209.6
Cement volume (m³)
0.84
Sand (m³)
1.26
Aggregate (m³)
2.52
Dry volume (m³)
4.62
Bags per cubic metre
8.06
How this is calculated
Method and background

How this is calculated

Multiply the wet volume by the dry factor to get the volume of loose ingredients, split that by the mix ratio, and convert the cement share to bags using a bulk density of 1440 kg per cubic metre. Every step is exposed because every one of them is a convention: the dry factor varies with the aggregate, cement density varies with how it has been stored, and the nominal mix ratios only apply to small works.

bags = wet volume * dry factor * cement share of the mix * 1440 kg/m3, divided by the bag weight
V
Wet concrete volume (m3)
k
Dry volume factor (ratio)
a:b:c
The mix ratio (ratio)

Full derivation: Concrete quantities, and where the 1.54 comes from

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

M20 at one cubic metre

Concrete volume (m³)
1
Mix grade
M20 (1:1.5:3)
Dry volume factor
1.54
Bag weight (kg)
50

Cement bags8.06

The familiar eight bags, derived rather than quoted

Open this example

a leaner mix needs less cement

Concrete volume (m³)
1
Mix grade
M10 (1:3:6)
Dry volume factor
1.54
Bag weight (kg)
50

Cement bags4.44

1 part in 10 rather than 1 in 5.5

Open this example

no volume needs no cement

Concrete volume (m³)
0.01
Mix grade
M20 (1:1.5:3)
Dry volume factor
1.54
Bag weight (kg)
50

Cement bags0.08

degenerate case

Open this example

Method and limits

What it assumes

  • Nominal mix ratios by volume, which is how small sites work.
  • Cement bulk density of 1440 kg per cubic metre.

What it deliberately does not model

  • A design mix for a specified strength is a laboratory exercise and does not follow these ratios.
  • Bulking of damp sand can add ten to thirty percent to the sand volume actually needed.

Sources

Formula version 1.0.0 · definition 1.0.0 · India · Report a problem with this calculator

Frequently asked questions

Why about eight bags per cubic metre for M20?
The dry volume is 1.54 m³, the cement share of 1:1.5:3 is one part in 5.5, so cement is 0.28 m³, which at 1440 kg/m³ is 403 kg, or 8.06 bags of 50 kg.