What this calculator does
Get a quick estimate of your share of the carbon dioxide (CO2) a flight puts out. Flying burns jet fuel, and each kilogram of fuel burned releases a set amount of CO2. Split a flight's total CO2 across its passengers and its distance. That gives an emission factor: kilograms of CO2 for each passenger for each kilometer (a passenger-kilometer). Multiply that factor by how far you fly, and you have your share of the flight's emissions.
The calculator shows that multiplication openly, step by step. You can enter a distance yourself. Or it can work out the great-circle distance (the shortest path over the globe) between two airports' coordinates. Every number that changes with the plane, airline, route or method is an input you control. Each has an example default you should replace with a figure from a source you trust.
Where it's used
Why this math matters outside the classroom:
- Travel choices. Travelers compare the CO2 of a flight with driving or rail for the same trip before booking.
- Company reporting. Companies add up staff flights to report business travel emissions in their sustainability reports.
- Great-circle routes. Geography students use the haversine formula to see why routes from North America to Asia curve far to the north.
- Worked example. A 1,000 km flight at 0.15 kg CO2 per passenger-km comes to 150 kg per passenger before any cabin multiplier.
How to use it
- Choose whether to enter a distance or two airport locations. For locations, use decimal degrees (one number with a decimal point, not degrees and minutes). Make south latitudes and west longitudes negative.
- Enter the number of passengers and pick a cabin class, or set a custom cabin multiplier.
- Replace the example emission factor with one for your flight. If you like, set a non-CO2 multiplier above 1.
- Tick round trip if you're flying back. Then read the total, each passenger's share and the steps.
What the inputs mean
- Departure latitude
- Airport coordinates are listed on airport information pages and aviation charts. The example coordinates are two US airports roughly 1,786 km apart.
- Departure longitude
- West is negative.
- Cabin class (example weights)
- Premium seats take up more floor space. So methods that share a flight's emissions by floor area give those seats a bigger share. The listed weights are round examples. Different methods use different values, so choose Custom to enter the one your source uses.
- Emission factor (example: 0.15)
- The default of 0.15 kg CO2 per passenger-km is only an example of the rough size. Real factors vary with the type of plane, how full it is, how much cargo it carries and how long the flight is. Take-off and climb use a large share of the fuel on short trips. Government greenhouse gas inventories (official emissions reports) publish factors by flight length. Some airlines publish their own per-flight figures.
- Non-CO2 multiplier (optional; 1 = CO2 only)
- Planes also affect the climate in other ways at high altitude. Contrails (the white trails behind planes), water vapor and nitrogen oxides all add warming. Some methods multiply CO2 by a factor to roughly cover these effects. Others leave them out because the science is still uncertain. 1 counts CO2 only. With a higher value, the result is a CO2-equivalent estimate (all the warming, expressed as CO2), not CO2 alone.
Formula and method
a = sin²(Δlat ÷ 2) + cos(lat₁) × cos(lat₂) × sin²(Δlon ÷ 2) c = 2 × atan2(√a, √(1 − a)) distance (km) = 6,371 × c CO2 (kg) = distance × legs × passengers × emission factor × cabin multiplier total = CO2 × non-CO2 multiplier
The haversine formula gives the shortest distance between two points on a ball, called the great-circle route. In it, lat₁ and lat₂ are the two latitudes and lon is longitude. Δlat and Δlon (read "delta") are the differences between the two points. a is a middle result, and c is the angle between the points as seen from Earth's center. Multiplying c by the Earth's average radius of 6,371 km gives the distance. The formula stays accurate even for points very close together or nearly opposite.
Everything after the distance is plain multiplication. Legs is 2 for a round trip and 1 for one way. The emission factor turns passenger-kilometers into kilograms of CO2. Miles and nautical miles are converted exactly (1.609344 km and 1.852 km).
Worked example
One passenger flies 1,500 km one way in economy, using an example factor of 0.15 kg CO2 per passenger-km and no non-CO2 multiplier.
- Passenger-km: 1,500 km × 1 passenger = 1,500 pkm.
- CO2: 1,500 × 0.15 × 1 = 225 kg.
- With the example coordinates instead, the great-circle distance is 1,786.12 km, so a round trip is 3,572.24 km and 3,572.24 × 0.15 = 535.84 kg.
Result: The 1,500 km one-way economy flight comes to about 225 kg of CO2 (0.225 tonnes) with these inputs.
Understanding the result
Treat the result as an estimate of your share, not a measurement. The emission factor you choose matters more than any other input.
Business and first class results are higher because those seats get a bigger share of the flight's fuel. It's not that the plane burns more because of you.
Comparing two options with the same factor is more reliable than the single number on its own. For example, compare a direct flight with one that connects.
Assumptions and limitations
- The flight follows the great-circle route. Real routes are usually a little longer because of air traffic control and weather.
- The emission factor already includes how full the plane usually is, and any share of emissions its source gives to cargo.
- A round trip is exactly twice the one-way distance.
- No plane, airline or route data is built in. You enter every factor yourself.
- Taxiing, circling while waiting to land (holding patterns) and detours aren't added, unless your emission factor already includes them.
- The non-CO2 multiplier simplifies effects that depend on altitude, weather and time of day. Scientists are still working out what its right value is.
Frequently asked questions
Why do flight carbon calculators give such different answers?
They make different choices. They use different emission factors, cabin weights and load factors (how full planes are). Some add extra distance for detours, and they treat non-CO2 effects differently. This calculator makes each of these an input. So you can match the choices of any method you want to compare against.
What is the radiative forcing multiplier?
It's a rough way to count the extra warming from contrails, water vapor and nitrogen oxides at high altitude. Estimates of that extra effect vary widely. They depend on how warming is compared over time. So some methods use a multiplier of around 2, and others use none. Leaving it at 1 reports CO2 only.
Why are short flights often worse per kilometer?
Taxiing, take-off and climbing to cruising height use a lot of fuel. On a short flight, that fuel is spread over fewer kilometers. So many published factors are higher for short flights than for long ones.
How accurate is the haversine distance?
It treats the Earth as a perfect ball. The real Earth is slightly flattened, but the answer is still within about half a percent. That error is much smaller than the uncertainty in any emission factor.
How this calculator is checked
Method: Haversine great-circle distance with mean Earth radius 6,371 km; CO2 = passenger-km × user emission factor × cabin and non-CO2 multipliers. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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