Free Electricity Carbon Footprint calculator with clear step-by-step results.
Metered consumption understates generation, because roughly 5-10% of electricity is lost in transmission and distribution before it reaches you. Grossing consumption up for those losses, removing any certified renewable share and applying grid intensity gives the emissions genuinely attributable to your supply.
Attributable generation
Gross kWh = metered kWh x (1 + T&D losses) x (1 - renewable share)
Footprint
kgCO2e = gross kWh x grid intensity / 1000
National grid operators and energy regulators publish it, and it varies enormously - under 50 gCO2e/kWh in hydro or nuclear-dominated grids and over 700 in coal-heavy ones.
Under market-based accounting, a certificate-backed tariff does reduce reported emissions. Under location-based accounting it does not, because the physical electrons come from the same grid mix.