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Concrete calculator

This calculator calculates the amount of concrete bag to buy to make a slab, deck, stairs or concrete foundations. Indicate the dimensions in length, width, height / thickness desired as well as the type of bag and its density.

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Concrete calculation formula

Calculate the slab volume

Slab Volume = Length x Width x Height / Thickness

Calculate the number of bags

Number of bags = Density of the concrete * Volume of the slab / Weight bag

The loss is then calculated by adding the defined% to the total.

The weight of concrete

Here is the table showing the different types of concrete as well as the density or weight per cubic meter (m3).

The weight of concrete depends on the density of the materials and the amount of air it contains.

Type of concrete Metric density Imperial Density
Mix bag 2130 kg / m3 (2110 kg / m3 to 2150 kg / m3) 133 lbs / ft3 (130 lbs / ft3 to 135 lbs / ft3)
For structure 2300 kg / m3 (2240 ??kg / m3 to 2400 kg / m3)
Reinforced concrete (ex slab or counter) 2400 kg / m3 (2300 kg / m3 to 2500 kg / m3)

Concrete mixes normally require about 1 liter per +/- 13 kg of concrete mix. For a 40kg bag we are talking about +/- 3 liters of water.

Concrete preparation

The preparation of concrete involves the mixing of materials such as: cement, sand, gravel and water. Under certain circumstances, the addition of metal or plastic materials may increase the strength of concrete slabs. Reinforced concrete is a good example.

Concrete dosages

Dosages are not specifically defined for all types of work. However, volume approximations give this:

Concrete in volume

Type of construction Cement Sand Gravel Water
Foundation or terrace 1 2.5 (2.25 to 2.75) 3.5 (3.25 to 3.75) 0.5 (0.4 to 0.6)
Concrete for post setting 1 2 (1.75 to 2.25) 3 (2.75 to 3.25) 0.5 (0.4 to 0.6)

A simple way to measure dosages in concrete is to go as follows: 1 serving of cement, 2 servings of sand, 3 servings of gravel and 1/2 of water

Concrete in kg

Type of construction Cement Sand Gravel Water
Concrete for foundation or terrace 350kg 825kg (800kg to 850kg) 1200kg (1150kg to 1250kg) 175kg (1kg = liter)
Concrete for post setting 350kg 700kg (675kg to 725kg) 1050kg (1000kg to 1100kg) 175kg (1kg = liter)

In all cases, it is better to add a surplus of 10-15% to consider the loss during concrete work.


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