Green Airlines

Rankings / Routes / Chicago to San Francisco

2025 flights

Chicago to San Francisco

Between Chicago and San Francisco, 2.4 million passengers flew nonstop in 2025, on 14 thousand flights of about 1,845 miles and 3.9 hours in the air. The average passenger accounted for about 235 kg of CO2 from the fuel burned, from 215 kg on Alaska Airlines to 242 kg on American Airlines.

  • 235 kgCO2 per passenger, average
  • 1,845 milesabout 3.9 hours in the air
  • 2.4 millionpassengers in 2025
  • 87%of seats filled

CO2 per passenger, airline by airline

CO2 per passenger by airline, Chicago to San FranciscoBar chart of kilograms of CO2 per passenger on each airline between Chicago and San Francisco in 2025.0100200Alaska Airlines215 kgSouthwest Airlines224 kgUnited Airlines237 kgAmerican Airlines242 kg
CO2 per passenger by airline, Chicago to San FranciscoBar chart of kilograms of CO2 per passenger on each airline between Chicago and San Francisco in 2025.0100200Alaska Airlines215 kgSouthwest Airlines224 kgUnited Airlines237 kgAmerican Airlines242 kg
Kilograms of CO2 per passenger, one way, 2025. Fuel burned only. Less is better.
Chicago to San Francisco by airline, 2025
AirlineShare of passengersFlights (thousands)Main aircraftSeats per flightSeats filledkg CO2 per passenger
United Airlines62%7.8Airbus A321neo, Boeing 757-30021787%237
American Airlines20%3.0Boeing 737-800, Airbus A32117588%242
Southwest Airlines15%2.5Boeing 737 MAX 8, Boeing 737-80016785%224
Alaska Airlines3%0.4Boeing 737-900ER, Boeing 737 MAX 917788%215

What explains the differences

It's number 50 of the 100 busiest city pairs by passengers, and number 9 for the lowest CO2 per mile flown (0.13 kg per passenger-mile, number 1 being the lowest). A typical route of 1,845 miles in this set comes out at about 255 kg, so this one is 7.8% below it.

The flights use more than one pair of airports: ORD to SFO (82%), MDW to SJC (6%), MDW to OAK (5%). The figures here cover all of them.

The airlines on this route differ by 12% per passenger. Alaska Airlines burned 3,442 gallons per flight and 156 passengers on each, and American Airlines 3,840 gallons and 155 passengers. Fuel burned per flight explains about 94% of the gap and the number of passengers on each flight the other 6%. Alaska Airlines flew 88% full here against 88% for American Airlines, 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 238 kg. The EPA figure is a national average for flights of that length. The measured figure for this route is 1.1% lower.

2019 compared with 2025

In 2019 the route carried 3.1 million passengers on 19 thousand flights. In 2025 it carried 2.4 million, down 23%, on 14 thousand flights, down 28%. The average flight had 184 seats then and 198 now, and 87% of them were filled against 87%.

CO2 per passenger was 258 kg in 2019 and 235 kg in 2025, down 8.6%. Fuel burned per flight was down 1.9% (4,241 gallons to 4,159) and passengers per flight were up 7.3% (160 to 172). The distance flown was about the same (1,844 miles then, 1,845 now).

United Airlines led in both years, with 53% of passengers in 2019 and 62% in 2025. Southwest Airlines lost the most, 20% to 15%. Spirit Airlines no longer reaches 1% of passengers, having had 1% in 2019.

Airline by airline, United Airlines went from 262 kg to 237 kg per passenger (209 seats per flight to 217, main aircraft Boeing 757-300 then and Airbus A321neo now); Southwest Airlines went from 234 kg to 224 kg per passenger (163 seats per flight to 167, main aircraft Boeing 737-800 then and Boeing 737 MAX 8 now).

The airports changed too: ORD to SFO handled 69% of the passengers in 2019 and 82% in 2025.

Chicago to San Francisco, 2019 and 2025
Measure20192025
Passengers (thousands)3,0952,378
Flights (thousands)19.313.8
Seats filled87%87%
Gallons of fuel per flight4,2414,159
kg CO2 per passenger258235
CO2 per passenger by airline, 2019 and 2025, Chicago to San FranciscoBar chart of kilograms of CO2 per passenger on Chicago to San Francisco for each major airline in 2019 and in 2025.0100200United Airlines 2019262 kgUnited Airlines 2025237 kgAmerican Airlines 2019264 kgAmerican Airlines 2025242 kgSouthwest Airlines 2019234 kgSouthwest Airlines 2025224 kgAlaska Airlines 2019280 kgAlaska Airlines 2025215 kg
CO2 per passenger by airline, 2019 and 2025, Chicago to San FranciscoBar chart of kilograms of CO2 per passenger on Chicago to San Francisco for each major airline in 2019 and in 2025.0100200United Airlines 2019262 kgUnited Airlines 2025237 kgAmerican Airlines 2019264 kgAmerican Airlines 2025242 kgSouthwest Airlines 2019234 kgSouthwest Airlines 2025224 kgAlaska Airlines 2019280 kgAlaska Airlines 2025215 kg
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 San Francisco and back: time in the air

Flights from Chicago to San Francisco spent 247 minutes in the air on average in 2025, against 218 minutes from San Francisco to Chicago: 29 minutes longer, 14% 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 1,074 gallons per flight hour, those extra minutes cost about 526 gallons per flight, which is about 3.1 gallons or 30 kg of CO2 for each passenger on the slower direction. The route figure above averages both directions.

Time in the air by direction, 2025
DirectionAverage minutes in the airFlights
Chicago to San Francisco246.96,926
San Francisco to Chicago217.56,885

Fly or drive

Driving is about 2,159 miles by road, which we estimate as 1.17 times the straight-line distance. An average car emits about 641 kg of CO2 on the trip, at the EPA figure of 0.297 kg per vehicle-mile. Alone, that's 172% more than the 235 kg for a passenger on the flight.

With 3 people in the car, driving comes out lower per person than the flight (214 kg each, and 160 kg each for four). A larger SUV or pickup (0.394 kg per mile) would emit about 851 kg per vehicle.

CO2 per person by way of travel, Chicago to San FranciscoBar chart of kilograms of CO2 per person flying, driving or taking the train between Chicago and San Francisco.0200400600Flight, average235 kgCar, driver alone641 kgCar, 2 people321 kgCar, 4 people160 kg
CO2 per person by way of travel, Chicago to San FranciscoBar chart of kilograms of CO2 per person flying, driving or taking the train between Chicago and San Francisco.0200400600Flight, average235 kgCar, driver alone641 kgCar, 2 people321 kgCar, 4 people160 kg
CO2 per person, Chicago to San Francisco. 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

Los Angeles to San Francisco75 kg CO2 per passenger over 337 milesNew York to Chicago125 kg CO2 per passenger over 730 milesSan Francisco to Las Vegas71 kg CO2 per passenger over 404 milesLos Angeles to Chicago225 kg CO2 per passenger over 1,739 milesNew York to Las Vegas284 kg CO2 per passenger over 2,239 milesDallas-Fort Worth to Seattle211 kg CO2 per passenger over 1,660 milesChicago to Seattle220 kg CO2 per passenger over 1,722 milesChicago to Las Vegas194 kg CO2 per passenger over 1,516 miles

Airports on this route: O'Hare International Airport, San Francisco International Airport, Midway International Airport, San Jose International Airport, Oakland San Francisco Bay 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.