How to calculate a product carbon footprint, step by step
Calculating a product carbon footprint comes down to one sum repeated many times: how much of something was used, multiplied by the emissions per unit of it. The work is in choosing what to count, finding the quantities and picking the right factors. Here are the steps in the order you would take them.
8 min read · Updated
- 1Choose the unit
- 2Set the boundary
- 3List the materials
- 4Measure factory energy
- 5Add transport and packaging
- 6Apply emission factors
- 7Check and report
1. Choose the unit
Decide what one footprint describes: one T-shirt, one pair of shoes, one shipping box or one kilogram of fabric. Buyers usually want one piece of what they buy from you. Record its weight, because many later steps scale with it.
2. Set the boundary
Decide which life-cycle stages are in. Footprints shared between companies under the PACT methodology are cradle to gate: everything up to the moment the product leaves your factory. A cradle-to-grave footprint adds distribution, use and end of life. See cradle to gate vs cradle to grave.
3. List the materials
Write down every material in one unit with its weight, including what is lost as waste in cutting and processing. For a T-shirt that is the fabric (and its fibre), thread, labels and any trims; for a box, the board and the ink. Note where each material comes from and how much is recycled.
4. Measure factory energy
Take a year of electricity and fuel bills for each process (spinning, knitting, dyeing, cutting and sewing) and divide by what the factory produced in that year. This gives energy per product. Your own metered figures are worth the most here, because they are primary data; see primary vs secondary data.
5. Add transport and packaging
Count how materials travel to you (distance and mode: truck, ship, air) and the packaging the product leaves in. Air freight is reported separately under PACT.
6. Apply emission factors
Multiply each quantity by an emission factor: the published emissions per kilogram of material, per kilowatt-hour of electricity in that country or per tonne-kilometre of freight. Factors come from national datasets, industry studies and databases; emission factors explained shows where ours come from.
Add up every line. That total, in kg CO₂e per unit, is the footprint.
7. Check and report
Before you send the figure, check the method: is anything left out, and is it small? Are the data quality scores reported? Is the uncertainty range stated? A footprint calculated with the ISO 14067 method comes with a report listing the boundary, data, assumptions and limitations, and a buyer may also want the PACT data file.
You can do all of this in a spreadsheet, or start from a product link in our tool and add your own data in the full footprint form, which runs the checks for you.
Questions
How long does a product carbon footprint take?
With the materials list and a year of energy bills to hand, a first footprint takes minutes in a tool. Collecting the data is usually the slow part.
Do I need my suppliers' data?
Not to start. Database factors fill the gaps, and the footprint reports how much of it is your own data, so you can improve it over time.
Can I calculate a footprint in Excel?
Yes: each line is quantity × factor. The hard parts are choosing defensible factors and documenting the method the way buyers expect.