How should figures be rounded for the UK CBAM?
Round emissions to the nearest whole tonne of CO2e for reporting, and only after every calculation is done. While calculating, record significant values to up to 5 decimal places, adding trailing zeros where needed. The emissions intensity of a good is rounded to 5 decimal places.
The rules
- Reported emissions: whole tonnes of CO2e.
- When: only after all calculations are complete.
- Working values: up to 5 decimal places, with trailing zeros where fewer are available.
- Emissions intensity: tonnes of CO2e divided by tonnes produced, rounded to 5 decimal places.
- How many decimals you can justify depends on the accuracy of your measuring equipment.
Where early rounding goes wrong
Rounding a fuel total or an installation total before you divide by production changes the intensity your buyer reports. Verifiers check the arithmetic, and a spreadsheet that rounds in the middle is a common finding.
Weight is separate
The net weight your buyer reports is in kilograms, with its own rounding rule. Keep the two apart.
Same data, two answers
- Total emissions for the product: 21,437.48291 tCO2e. Production: 10,000 t.
- Right: 21,437.48291 / 10,000 = 2.1437483, rounded to 2.14375 tCO2e/t. Report 21,437 tCO2e.
- Wrong: round first to 21,437, then 21,437 / 10,000 = 2.14370 tCO2e/t.
- On 2,000 t imported, the gap is 0.1 tCO2e; across a year of shipments it adds up.
Example figures.
What Senseible does here
Senseible keeps the unrounded quantities read from each invoice, so totals are not rounded before the final step. We build the figure from your records and check every figure in-house; for the UK it must then be verified by a verifier accredited for UK CBAM. Have your own verifier? Send it to them.
Sources: HMRC, UK CBAM monitoring, reporting and verification technical guidance (October 2026), HMRC, Carbon Border Adjustment Mechanism (CBAM): Policy summary (updated 2 November 2026)
Last reviewed 2026-11-03.