Directly: MWh of fuel saved × your fuel emission factor (default 0.183 t CO2e/MWh — natural gas, UK DESNZ 2024) + MWh of electricity saved × your grid factor (default 0.25 t/MWh, editable — it varies by country and year). No currency round-trip. The carbon value is that tonnage at the live EU ETS price shown on this hub.
From our guide: Universal Industrial Savings Calculator — full context, charts and sources there.