Goal: Bring data into weight-based units (tonnes) for the same reference year.

Situation: There is some data that requires additional calculations for conversion to meet the goal, such as:

  • Data in weight-based unit: If the data is already in a weight-based unit, but a different weight than you desire, for example in kg or in megatonnes, then you need to multiply or divide by 1000 accordingly to convert to tonnes, which is typically the standard common unit to aim for.
  • Data in non-weight-based unit: There are many instances where the data is not yet in a weight-based unit and also needs to be converted to tonnes, for example, when it is in:
    • Volume
    • Monetary value, expressed in Euro or Dollars
    • Length of road network or railways
    • Hectares (without yields), for agricultural production
    • “Heads” of animals
  • Data that has other reference year: It is well possible that you have data available for a year other than your reference year.


You then need to convert this data with additional calculations, usually requiring additional data and multiplications.

Example 1: Volume of wood

  • In the case of wood, the unit of harvest is often volume.
  • In order to convert it to weight, the wood density is needed
    • Tree functional attributes and ecological databases’ wood density overview
    • [Forest Research UK](]
    • example of Finland: “The main tree species in Finland are pine, spruce and birch. Pine and spruce are the most common in construction. The density of Finnish pine is 370 – 550 kg/m3, spruce 300 – 470 kg/m3 and birch 590 – 740 kg/m3.” Source
    • Different wood products in Finland and their density, Source
  • The wood density can be multiplied with the volume of the wood to obtain the weight of the wood.

Example 2: Length of road network or railways

  • Data for Road network in Mikkeli
  • the data is given in km to represent the length of roads, but it needs to be converted to tonnes to determine the weight of the materials.
  • the Economy-wide material flow accounts handbook has some values from Germany on tonnes of sand and gravel used for construction and maintenance of different types of roads.
    • With this, it’s possible to calculate the materials needed for construction of Mikkeli roads.
    • However, the years of construction of Mikkeli’s road are not mentioned and would also be needed so that a calculation could be made of material flows used for maintenance.

More data exists also for other countries. Here for example, for the United States, “Modeling material flows and stocks of the road network in the United States 1905–2015”, (Table 1, see below)

Type of road Rammed earth (t/km) Gravel (t/km) Sand (t/km) Cement (t/km) Bitumen (t/km) Total (t/km)
Unsurfaced pavement 32 0 0 0 0 32
Unpaved pavement 0 231 0 0 0 231
Low type pavement 0 444 0 0 4 447
Intermediate pavement 0 1722 0 0 11 1732
High flexible pavement 0 4607 0 0 27 4634
High composite pavement 0 3260 1728 522 19 5528
High rigid pavement 0 2862 1958 592 0 5412

Example 3: Hectares of crop

  • Sometimes the data is only given in a surface area, for example those of the agricultural production of crops on a field.
  • In this case, you need the crop yield (kg/ha), which is the weight of crops that can be grown or harvested (depending on the definition) on a given surface area.
  • Having the crop yield, you can multiply it by the hectares of the respective fields to obtain the weight of the crop.

Example 4: Heads of animals

  • Animal data is sometimes provided by number of animals, which is termed as “heads”.
  • There is usually a range of weight of the animals, depending on their type, gender and age.
  • A table on the average weight of animals (kg/head) can help to determine the weight of the animals
    • The “Working Group Animal Production Statistics” provides such a table for Eurostat, see below. Source

Note: Sometimes you might have data that is not in the nomenclature that you need. In this case you can have a look at this useful image that shows the different nomenclatures and their relationships: “What links to what”.

Outline of the video

  • 0:05 What is conversion? Whenever you do a material flow analysis or a circularity assessment of a city or of a sector, what you want to do is to measure stuff in tonnes or in kilogrammes or in mass terms. Our goal here is to be able to compare flows one with another. So if you have flows in different units, then it's not possible.
  • 0:32 main challenge you're gonna find data in different units.
    • Sometimes you're gonna find animals in terms of heads, how many heads you have in your forest or in a particular city
    • you might be able to find how much road network or rail network you have but not in kilograms, but instead in terms of length.
    • some imports and exports are also reported in monetary terms in Euros and dollars.
    • sometimes you know waste flows or waste water flows or water flows are measured in cubic metres or in litres.
  • 1:19 How to solve the problem We try to find conversion factors. We try to convert from whatever other unit is to a material unit. So a mass unit in terms of kilograms, tons kilotons.
  • 1:39 two examples
    • one example in the case of Bodø, Norway, where what we had was the number of cubic metres of roundwood that was harvested every year. So we went about and looked for conversion factors.
    • 2:29 So sometimes for instance, the European commission provides these and this is for instance, in the case of how much animals weigh. So over here there is a table that kind of gives you a minimum and maximum range of mass per type of animal.
  • 3:33 How to get to tonnes Well, you just multiply the two in order to get to tonnes. If I have the number of bulls that exist in my city or, or that are killed for, to enter within the economy, I would just multiply this by the mean between the two, the mean between the min and the max or have a range. So if it's 100 times 130 kg, it would be 13 tonnes.