Greenhouse Gas Inventory Calculator

This calculator uses the US national average grid factor of 0.388 kg CO₂ per kWh, approximating the national annual average total-output CO2 rate EPA's eGRID2022 dataset publishes (823.1 lb CO2/MWh, grossed up for transmission and distribution losses), not your specific utility or region's actual generation mix. If your grid leans heavily on coal, your real emissions are higher than this estimate; if it leans on hydro, nuclear, or wind, your real emissions are lower. For a compliance-grade inventory, look up your own eGRID subregion's published rate and substitute it for the 0.388 constant used here.

This calculator only covers two Scope 3 categories — air travel (0.255 kg CO₂/passenger-mile) and employee commuting (0.346 kg CO₂/vehicle-mile) — out of the 15 categories the GHG Protocol defines. A complete Scope 3 inventory also includes purchased goods and services, capital goods, waste, upstream transportation, and more, which typically dwarf travel and commuting for most organizations. Treat this tool's Scope 3 figure as a partial estimate, not a full accounting.

The calculator multiplies your total CO₂e (all three scopes summed) by a flat $30 per metric ton, which is the midpoint of a typical $15–50/ton voluntary carbon offset price range. Actual offset pricing varies widely by project type, verification standard, and market conditions, so this is meant as a rough budgeting placeholder rather than a quote from any specific offset provider.

Natural gas is converted using 53.06 kg CO₂ per MMBtu of energy content, while diesel uses 10.21 kg CO₂ per gallon burned — two different units (energy versus volume) reflecting how each fuel is typically metered. Because MMBtu and gallons aren't directly comparable, the calculator converts both into the same metric-tons-CO₂e unit before summing them into Scope 1, so you can see each fuel's contribution on equal footing in the results.