How do I split emissions between two products that come out of the same process?
Follow the ISO 14044 order. First avoid splitting, by dividing the process or by system expansion. If you cannot, split by a physical relationship, usually mass. Use economic value only when no physical link reflects how the process works. Whatever you choose, the product shares must add back to the process total.
What counts as a co-product
A co-product is a second output with value that the same process produces unavoidably: bran and husk from milling rice, secondary or cut-length steel from a rolling mill, molasses from sugar. An output with no value that you pay to dispose of is waste, not a co-product, and carries no share of the emissions.
The three steps, in order
This hierarchy is ISO 14044:2006 clause 4.3.4. ISO 14067:2018 and the GHG Protocol Product Standard follow it.
- Avoid allocation. Subdivide the process if a step serves only one product, for example a polisher used only for rice. Or expand the system: credit the main product with what the co-product replaces elsewhere, if you can show that substitution.
- Allocate by a physical relationship that reflects how the inputs and emissions change with the outputs, most often mass, sometimes energy content.
- Allocate by another relationship, usually economic value, when no physical link is meaningful, such as when the co-product is a small, low-value share of mass.
Rules auditors check
- Apply the same method to similar inputs and outputs, and keep it from year to year.
- When more than one method looks reasonable, ISO 14044 asks for a sensitivity check: show the result under the alternative and explain the choice.
- For economic allocation, use average prices over a stated period, not one month's spot price.
Worked example: a rice mill, one month
- Process total: 60,000 kWh x 0.710 = 42,600 kg CO2, plus 1,000 L diesel x 2.68 = 2,680 kg CO2; total 45,280 kg CO2
- Outputs: 400 t milled rice and 40 t bran (husk left out to keep the example short)
- By mass: rice 400/440 = 90.9%, 41,164 kg; bran 4,116 kg; both 102.9 kg CO2 per tonne
- By value (illustrative prices ₹30,000/t rice, ₹15,000/t bran): rice ₹1.20 crore, bran ₹6 lakh, total ₹1.26 crore
- Rice 95.2%, 43,124 kg, 107.8 kg CO2 per tonne; bran 4.8%, 2,156 kg, 53.9 kg CO2 per tonne
- Check: 41,164 + 4,116 = 45,280 and 43,124 + 2,156 = 45,280
A real mill also has husk, broken rice and often its own husk-fired boiler; each changes the split, so state what you included.
What Senseible does here
Senseible gives the process total from fuel and electricity bills, such as the month's Scope 1 and 2 above. The split between co-products is your documented choice; Senseible does not allocate emissions to products.
Sources: ISO 14044:2006 clause 4.3.4, allocation; ISO 14067:2018, Carbon footprint of products, GHG Protocol Product Life Cycle Accounting and Reporting Standard (2011), chapter 9
Last reviewed 2026-10-15.