Life Cycle Assessment
Primary vs Secondary Data: Which and When?
The difference between primary (measured) and secondary (database) data in LCA and DPP work, how data quality is assessed and which to use where.
The credibility of an environmental calculation rests on the type of data behind it. There are two categories: primary data, which you or your supplier measured, and secondary data, average values from databases or literature.
The difference
| Primary data | Secondary data | |
|---|---|---|
| Source | Meters, production records, supplier declarations | Databases, literature, sector averages |
| Accuracy | High (site-specific) | Medium (average) |
| Cost | High (collection effort) | Low |
| Currency | Under your control | Tied to database version |
Where primary data is essential
- Energy consumption at your own site (electricity, gas, steam).
- Material quantities and scrap rates.
- Inputs from direct suppliers that dominate the result.
The general rule: target primary data for the items making up 80% of emissions. See how to calculate a PCF.
Where secondary data is reasonable
- Distant background processes (crude extraction, basic chemical production).
- Components with small contributions.
- A temporary baseline for items where supplier data does not exist yet.
Assessing data quality
| Dimension | Question |
|---|---|
| Temporal | How old is the data? |
| Geographic | Same country or grid region? |
| Technological | Same production technology? |
| Completeness | Does it cover all the processes? |
Scoring and reporting these four is the practice that helps most in an audit.
A strategy for getting primary supplier data
- Build a baseline with secondary data and see which items dominate.
- Go to suppliers only for those items — a six-field request, not a forty-page questionnaire.
- Standardise the template; a bespoke form per customer exhausts suppliers.
- Put it in the contract. See DPP clauses for supplier contracts.
See collecting data from suppliers and tier-2 and tier-3 transparency.
Declaring it in the passport
Stating the data type beside an environmental field is a stronger credibility signal than the number itself. "Carbon footprint: 4.2 kg CO2e (primary site data, 2026)" is far more defensible than a figure with no provenance. See DPP data quality management.
Frequently asked questions
Is using secondary data non-compliance?
No. Methodologies explicitly accept it; the condition is that its use is declared.
Do I need a database licence?
Commercial LCA databases are licensed. Some national inventories and sector averages are free and can be enough to start.
How often should I update the data?
Whenever the energy mix, a supplier or a process changes. Otherwise an annual review is a reasonable rhythm.
