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Tonnage Calculator

Tonnage Calculator

Tonnage Calculator:  What is a tonnage?

The word “tonnage” itself can mean a lot of things. We can use tonnage to describe the sizing of an HVAC system or how much a ship weighs. Basically, tonnage is the weight in tonnes (or tons for short) of massive volume objects, such as the contents of a cargo ship or earthworks like rocks and gravels.

This calculator focuses on the latter, particularly the different aggregates used in construction. We use these aggregates as bedding materials, subgrade, and subbase of pavements and slabs on the ground or as a part of mixtures like concrete or asphalt. Each kind of aggregate has its own unit weight that we can utilize to estimate its tonnage.

How to calculate the tonnage of aggregates

Learning how to calculate rock tonnage is an invaluable but easy skill, and it is essential when estimating project costs and even buying construction materials. Finding the tonnage of specific materials such as aggregates is a matter of multiplying its occupied volume by its unit weight. We can express that in equation form as follows:

𝑊=𝑉×𝛾×0.001 tons/kg


  • 𝑊 – Tonnage of aggregates (in tons, of course);
  • 𝑉 – Aggregates’ volume (in cubic meters); and
  • 𝛾 – Aggregates’ unit weight (in kilograms per cubic meter).

Multiplying 𝑉×𝛾 with 0.001 tons/kg converts 𝑉×𝛾 from kilograms to tonnes.

Note that if you know your aggregates’ unit weight in pounds per cubic foot (lb/ft3), you must instead use your aggregates’ volume in cubic feet (ft3) in the formula above. Then, you have to multiply the outcome by 0.453592 kg/lb to convert it to tonnes.

When finding the volume of aggregates, we usually take the area that our aggregates will cover and multiply that value by how deep we want our aggregates to be. In equation form, we have that as:



  • 𝑉 – Volume of the aggregates;
  • 𝐴 – Area of the surface we want to cover; and
  • 𝑑 – Depth of the aggregate cover.

Usually, the area we want to cover has a rectangular shape where we can obtain its area by multiplying its length by its width, as shown below:



  • 𝐴 – Area of the surface we want to cover;
  • 𝑙 – Length of the surface; and
  • 𝑤 – Width of the surface.

Of course, there will be times when the area you want to cover may not be rectangular.

Tonnage Calculator:

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