Calculate intensity from a matched numerator and denominator
To calculate a combined intensity, add the underlying quantities before dividing. Averaging site ratios gives each site equal weight, even when one produces twice as much as another. Before either calculation, check that the numerator and denominator cover the intended operations, period and measurement basis.
This guide helps reporting and finance teams prepare an environmental intensity calculation. The worked example uses energy per tonne of output; other metrics need their own definitions and applicable reporting requirements.
Define what each side of the ratio measures
Write the numerator in words, with its unit: for example, total energy consumed within the two reporting sites, in gigajoules (GJ). Then make a six-field denominator record:
Metric: precisely what is counted, such as tonnes of finished product rather than tonnes of raw material handled.
Population: the sites, entities and activities included, matched to the numerator's intended boundary.
Period: start and end dates, including any missing months.
Unit and basis: metric tonnes, product definition and any conversions; for monetary measures, the currency and scale.
Evidence: source record, data owner and reconciliation to the approved total.
Exceptions: estimates, exclusions, corrections and unresolved gaps, with their effect on the calculation.
This record is an optional working method, not a prescribed reporting template. For example, dividing energy from Sites A and B by production from A, B and C would introduce unsupported output into this two-site metric. A full-year numerator paired with nine months of production creates a different mismatch. Resolve or explicitly limit the calculation before interpreting it.
Combine the quantities before calculating the ratio
Consider two fictional sites with complete records for the same twelve months. They make the same defined product, use the same energy-accounting basis and report all relevant energy within their site boundaries. All figures are invented.
Site A: 40,000 GJ divided by 10,000 tonnes = 4 GJ per tonne.
Site B: 60,000 GJ divided by 5,000 tonnes = 12 GJ per tonne.
Combined: (40,000 + 60,000) GJ divided by (10,000 + 5,000) tonnes = 6.666… GJ per tonne, displayed as 6.67.
The simple average, (4 + 12) ÷ 2 = 8 GJ per tonne, answers an equal-weighted site question. It does not give the combined energy per tonne of output.
The denominator-weighted calculation gives the same result as the combined totals: [4 × 10,000 + 12 × 5,000] ÷ 15,000 = 6.666… GJ per tonne. Site A receives two-thirds of the weight because it accounts for two-thirds of output. Keep full precision until the final display.
This combination works because the quantities use compatible definitions and units. Do not pool tonnes with units sold, or different product categories merely because both are measured by weight, without establishing what the combined metric would mean.
Treat zero and missing values differently
A zero denominator makes the individual ratio undefined. If a temporarily idle site consumes energy but produces nothing, retain that energy in the numerator of a combined ratio when the site belongs in its boundary. The combined ratio can still be calculated if the combined denominator is positive. Dropping the site's energy would change the metric.
A missing denominator is unknown, not zero. Obtain the record or document a supported estimation approach under the applicable requirements. Until the gap is resolved, withhold the complete-boundary ratio or clearly label a genuinely matched subset and its exclusions. Never combine all-site energy with only the available production records.
Show absolute quantities beside the change in intensity
Extend the fictional example to a second complete year with unchanged coverage, definitions and units. Combined energy rises to 110,000 GJ and output rises to 18,750 tonnes.
Energy increases by (110,000 ÷ 100,000 − 1) × 100 = 10%.
Output increases by (18,750 ÷ 15,000 − 1) × 100 = 25%.
Intensity becomes 110,000 ÷ 18,750 = 5.866… GJ per tonne, displayed as 5.87.
The intensity change, using unrounded ratios, is (1.10 ÷ 1.25 − 1) × 100 = −12%.
Report both results: energy intensity decreased by 12%, while total energy consumption increased by 10%. Those figures alone do not establish an efficiency intervention's effect. For that separate question, see Separate energy savings from changes in production.
Check the reporting edition before using the calculation
Where GRI 302: Energy 2016 applies, Disclosure 302-3 requires the ratio, chosen denominator, energy types and whether consumption is within or outside the organisation. Its compilation requirements call for separate ratios when reporting both internal and external energy consumption. GRI 302, Disclosure 302-3
GRI 103: Energy 2025, Disclosure 103-4 explicitly includes the numerator alongside the ratio and denominator. Its guidance recommends a consistent organisational boundary for both sides. GRI 103, Disclosure 103-4
GRI 103 takes effect for reporting published on or after 1 January 2027; earlier adoption is encouraged. Check the intended publication date and reporting basis rather than relying only on the financial-year label. GRI 103 official FAQ, question 6
Prepare a calculation others can follow
Keep the source totals, denominator record, formula and rounding rule together. Nitium's sustainability and GRI reporting support helps organise data, draft content and information gaps within an agreed scope. Discuss your reporting needs with the metric, reporting period and a non-confidential description of the issue.
Sources checked 13 October 2026. The examples are fictional. This guide supports reporting preparation and does not constitute a complete GRI disclosure, legal opinion or independent assurance conclusion.
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