Dairy Carbon Footprint

This calculator uses the IPCC AR5 100-year global warming potential (GWP) for methane, which is 28 — meaning one pound of methane traps roughly as much heat over a century as 28 pounds of CO2, per the IPCC's Fifth Assessment Report (Working Group I, Chapter 8). Both enteric fermentation and manure methane get multiplied by this factor before being added to the total, which is why those two sources dominate the emissions breakdown even though the raw pounds of gas involved look small next to feed or energy figures.

Enteric methane is entered as a per-cow annual figure (defaulting to 264 lbs/cow/year) and multiplied straight through by herd size, then multiplied again by the GWP of 28, so it scales with herd size regardless of how efficiently the herd is managed. Manure and feed emissions scale the same way, but their per-cow defaults produce a smaller CO2e contribution once the same 28x methane multiplier or direct CO2e figure is applied — larger herds see enteric fermentation dominate the emissions breakdown almost by construction.

Annual milk is daily production per cow × herd size × 305 (a standard 305-day lactation length), then scaled again by 305/365 to approximate that not every cow is in active lactation for the entire calendar year. That double adjustment brings the milk-output denominator closer to a realistic whole-herd annual total, which directly affects the CO2e-per-gallon and CO2e-per-CWT figures — understating herd size or overstating daily milk will understate your true per-gallon footprint.

The energy input is collected as kWh per month because that matches how most farms read their utility bills, then internally multiplied by 12 to annualize it before applying the 0.86 lbs CO2/kWh US grid average. If your farm's actual electricity mix is cleaner or dirtier than the national average — for example, hydro-heavy or coal-heavy regional grids — the energy slice of your footprint will be over- or understated relative to reality.