Methodology & data sources

A Carbonnest result is an estimate produced from the activity data entered and a stated conversion factor or financial assumption. It is not a measurement of a specific power station, vehicle, flight or solar array. Each calculator states whether its result covers combustion, use-phase emissions or a wider lifecycle boundary.

We keep different boundaries visible because two correct factors can produce different answers. For example, a combustion-only gasoline factor excludes extraction and refining, while a lifecycle electricity factor includes upstream fuel and infrastructure emissions.

We prefer primary government publications for fuels and transport and transparent research datasets for global comparisons. A factor must identify its unit, geography, reporting year and boundary before it is added. Time-sensitive factors are reviewed when the source publishes its next annual release.

The current flight and UK rail values come from the revised UK Government 2026 conversion-factor set. US gasoline, therm and average-vehicle values follow the EPA equivalencies methodology. Electricity choices use Ember’s 2025 lifecycle grid-intensity dataset, published in 2026 and processed by Our World in Data so countries share one methodology.

Calculations use unrounded values internally. Display rounding happens only after the result is calculated. Distance conversion uses exactly 1.609344 kilometres per mile. Fuel conversion uses 3.785411784 litres per US gallon and 4.54609 litres per imperial gallon.

The EV calculator explicitly separates US and imperial mpg. It first converts distance and fuel to kilometres and litres, preventing the roughly 20% error caused by treating the two gallon definitions as interchangeable.

Electricity emissions equal kilowatt-hours multiplied by the selected kg CO₂e-per-kWh factor. Annual grid averages can differ from hourly, regional, utility or tariff-specific values, so both electricity tools accept a custom factor.

EV energy and petrol consumption are normalised to kWh and litres. Cost uses the prices entered in one local currency. Emissions use the selected lifecycle grid factor and a petrol factor that includes production and vehicle use. Vehicle and battery manufacture remain outside the comparison.

Passenger-kilometres equal one-way distance multiplied by trip legs and passenger count. The chosen haul and cabin profile supplies the flight factor. The non-CO₂ switch selects the Government value with or without radiative forcing; the published distance uplift is already included.

Rail uses the UK national-rail passenger average. It is a useful comparison for UK journeys, not a claim that every train worldwide has the same emissions. Route, traction energy and occupancy can materially change both modes.

First-year generation equals system kWp multiplied by annual kWh per kWp. Each later year applies the chosen degradation rate. On-site energy avoids the import price, exported energy earns the export rate, and maintenance is deducted annually. The payback point is interpolated within the first year in which cumulative cash flow becomes non-negative.

The projection is undiscounted and does not automatically include finance, tax, incentives, inverter or battery replacement. Those costs should be added to installed cost or annual maintenance, or assessed in a professional discounted-cash-flow model.

Pure calculation functions are covered by repeatable tests for invalid values, unit equivalence and multi-year cash flows. Inputs are constrained to finite, non-negative ranges before they reach charts or formulas.

Corrections are welcome. Send the calculator URL, input values, expected result and supporting source to bkapamulomo@bluecodeltd.com. We review the formula and source before changing a published factor.