Chicago to Seattle

Between Chicago and Seattle, 1.8 million passengers flew nonstop in 2025, on 12 thousand flights of about 1,722 miles and 3.7 hours in the air. The average passenger accounted for about 220 kg of CO2 from the fuel burned, from 205 kg on Alaska Airlines to 254 kg on Delta Air Lines.

220 kgCO2 per passenger, average
1,722 milesabout 3.7 hours in the air
1.8 millionpassengers in 2025
87%of seats filled

CO2 per passenger, airline by airline

Kilograms of CO2 per passenger, one way, 2025. Fuel burned only. Less is better.

Chicago to Seattle by airline, 2025

Airline	Share of passengers	Flights (thousands)	Main aircraft	Seats per flight	Seats filled	kg CO2 per passenger
Alaska Airlines	32%	3.6	Boeing 737-900ER, Boeing 737 MAX 9	176	88%	205
United Airlines	27%	3.1	Airbus A321neo, Boeing 737-800	175	89%	214
American Airlines	20%	2.2	Boeing 737-800, Airbus A321	180	87%	236
Delta Air Lines	12%	1.8	Boeing 737-800, Airbus A220-300	147	83%	254
Southwest Airlines	10%	1.2	Boeing 737 MAX 8, Boeing 737-700	165	87%	213

What explains the differences

It's number 84 of the 100 busiest city pairs by passengers, and number 10 for the lowest CO2 per mile flown (0.13 kg per passenger-mile, number 1 being the lowest). A typical route of 1,722 miles in this set comes out at about 240 kg, so this one is 8.4% below it.

The flights use more than one pair of airports: SEA to ORD (91%), SEA to MDW (10%). The figures here cover all of them.

The airlines on this route differ by 24% per passenger. Alaska Airlines burned 3,241 gallons per flight and 155 passengers on each, and Delta Air Lines 3,193 gallons and 123 passengers. The gap comes from how many passengers share each flight, not from fuel burned per flight. Alaska Airlines flew 88% full here against 83% for Delta Air Lines, flying mostly Boeing 737-900ER against Boeing 737-800.

For comparison, the EPA default factor for a flight of this length (0.129 kg per passenger-mile) would give 222 kg. The EPA figure is a national average for flights of that length. The measured figure for this route is 1.0% lower.

2019 compared with 2025

In 2019 the route carried 1.8 million passengers on 13 thousand flights. In 2025 it carried 1.8 million, down 3%, on 12 thousand flights, down 6%. The average flight had 163 seats then and 171 now, and 89% of them were filled against 87%.

CO2 per passenger was 237 kg in 2019 and 220 kg in 2025, down 7.3%. Fuel burned per flight was down 4.7% (3,533 gallons to 3,368) and passengers per flight were up 2.9% (145 to 149). The distance flown was about the same (1,722 miles then, 1,722 now).

Alaska Airlines led in both years, with 27% of passengers in 2019 and 32% in 2025. Spirit Airlines no longer reaches 1% of passengers, having had 2% in 2019.

Airline by airline, Alaska Airlines went from 228 kg to 205 kg per passenger (165 seats per flight to 176, main aircraft Boeing 737-900ER in both years); American Airlines went from 245 kg to 236 kg per passenger (162 seats per flight to 180, main aircraft Boeing 737-800 in both years).

Chicago to Seattle, 2019 and 2025

Measure	2019	2025
Passengers (thousands)	1,830	1,767
Flights (thousands)	12.6	11.8
Seats filled	89%	87%
Gallons of fuel per flight	3,533	3,368
kg CO2 per passenger	237	220

Kilograms of CO2 per passenger on the airlines that flew the route in both years. 2019 figures use that year's filings and estimated aircraft fuel rates, with type-average replacements for missing or outlying filings as described in the methodology. Less is better.

Chicago to Seattle and back: time in the air

Flights from Chicago to Seattle spent 237 minutes in the air on average in 2025, against 205 minutes from Seattle to Chicago: 33 minutes longer, 16% more. That's the westbound direction, into the prevailing west-to-east winds, which at flight levels often blow at well over 50 miles an hour.

At this route's average burn of about 914 gallons per flight hour, those extra minutes cost about 497 gallons per flight, which is about 3.3 gallons or 32 kg of CO2 for each passenger on the slower direction. The route figure above averages both directions.

Time in the air by direction, 2025

Direction	Average minutes in the air	Flights
Chicago to Seattle	237.3	5,927
Seattle to Chicago	204.7	5,911

Fly or drive

Driving is about 2,015 miles by road, which we estimate as 1.17 times the straight-line distance. An average car emits about 598 kg of CO2 on the trip, at the EPA figure of 0.297 kg per vehicle-mile. Alone, that's 172% more than the 220 kg for a passenger on the flight.

With 3 people in the car, driving comes out lower per person than the flight (199 kg each, and 150 kg each for four). A larger SUV or pickup (0.394 kg per mile) would emit about 794 kg per vehicle.

CO2 per person, Chicago to Seattle. Driving figures divide one car's emissions between the people in it. See flying vs driving for other trip lengths.

Flights are listed under the airline that operates them, so regional flying appears under the regional. How the CO2 and drive figures are worked out is in the methodology.

Routes with shared cities or nearby CO2 per mile

New York to Chicago125 kg CO2 per passenger over 730 miles Los Angeles to Seattle151 kg CO2 per passenger over 959 miles Los Angeles to Chicago225 kg CO2 per passenger over 1,739 miles Chicago to Washington, DC121 kg CO2 per passenger over 609 miles Dallas-Fort Worth to Seattle211 kg CO2 per passenger over 1,660 miles Chicago to San Francisco235 kg CO2 per passenger over 1,845 miles Chicago to Las Vegas194 kg CO2 per passenger over 1,516 miles

Airports on this route: Seattle-Tacoma International Airport, O'Hare International Airport, Midway International Airport.

Airport and airline references

Source: US Bureau of Transportation Statistics (BTS), T-100 traffic and Schedule T-2 fuel filings; US EPA transport emission factors. See the methodology.

See all routes, or how the airlines compare overall on the airline pages.