San Francisco to Seattle

Between San Francisco and Seattle, 3.1 million passengers flew nonstop in 2025, on 28 thousand flights of about 683 miles and 1.7 hours in the air. The average passenger accounted for about 119 kg of CO2 from the fuel burned, from 104 kg on Alaska Airlines to 174 kg on SkyWest Airlines.

119 kgCO2 per passenger, average
683 milesabout 1.7 hours in the air
3.1 millionpassengers in 2025
80%of seats filled

CO2 per passenger, airline by airline

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

San Francisco to Seattle by airline, 2025

Airline	Share of passengers	Flights (thousands)	Main aircraft	Seats per flight	Seats filled	kg CO2 per passenger
Alaska Airlines	46%	10.3	Boeing 737-900ER, Boeing 737 MAX 9	172	81%	104
Southwest Airlines	18%	4.6	Boeing 737-700, Boeing 737 MAX 8	159	76%	114
United Airlines	17%	4.2	Airbus A320-200, Airbus A319	156	80%	117
SkyWest Airlines	11%	5.6	Embraer 175	73	83%	174
Delta Air Lines	5%	1.7	Boeing 737-800	130	71%	137
Horizon Air	4%	1.6	Embraer 175	76	90%	148

What explains the differences

It's number 22 of the 100 busiest city pairs by passengers, and number 73 for the lowest CO2 per mile flown (0.17 kg per passenger-mile, number 1 being the lowest). A typical route of 683 miles in this set comes out at about 113 kg, so this one is 5.8% above it.

The flights use more than one pair of airports: SEA to SFO (52%), SEA to SJC (30%), SEA to OAK (18%). The figures here cover all of them.

The airlines on this route differ by 67% per passenger. Alaska Airlines burned 1,480 gallons per flight and 139 passengers on each, and SkyWest Airlines 1,092 gallons and 61 passengers. The gap comes from how many passengers share each flight, not from fuel burned per flight. Alaska Airlines flew 81% full here against 83% for SkyWest Airlines, flying mostly Boeing 737-900ER against Embraer 175.

For comparison, the EPA default factor for a flight of this length (0.129 kg per passenger-mile) would give 88 kg. The EPA figure is a national average for flights of that length. The measured figure for this route is 35% higher.

2019 compared with 2025

In 2019 the route carried 4.4 million passengers on 39 thousand flights. In 2025 it carried 3.1 million, down 29%, on 28 thousand flights, down 28%. The average flight had 142 seats then and 139 now, and 79% of them were filled against 80%.

CO2 per passenger was 127 kg in 2019 and 119 kg in 2025, down 6.0%. Fuel burned per flight was down 6.8% (1,458 gallons to 1,359) and passengers per flight were down 0.9% (112 to 111). The distance flown was about the same (683 miles then, 683 now).

Alaska Airlines led in both years, with 46% of passengers in 2019 and 46% in 2025. SkyWest Airlines gained the most share, 2% to 11%. Delta Air Lines lost the most, 11% to 5%. Compass Airlines no longer reaches 1% of passengers, having had 4% in 2019.

Airline by airline, Alaska Airlines went from 118 kg to 104 kg per passenger (161 seats per flight to 172, main aircraft Boeing 737-900ER in both years); Delta Air Lines went from 142 kg to 137 kg per passenger (122 seats per flight to 130, main aircraft unlisted aircraft then and Boeing 737-800 now).

San Francisco to Seattle, 2019 and 2025

Measure	2019	2025
Passengers (thousands)	4,389	3,119
Flights (thousands)	39.1	28.0
Seats filled	79%	80%
Gallons of fuel per flight	1,458	1,359
kg CO2 per passenger	127	119

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.

San Francisco to Seattle and back: time in the air

The time in the air is almost the same each way: 101 minutes on average from San Francisco to Seattle and 102 minutes back. A difference of 2 minutes is within what routing and congestion alone produce.

Time in the air by direction, 2025

Direction	Average minutes in the air	Flights
Seattle to San Francisco	102.2	14,014
San Francisco to Seattle	100.5	13,993

Fly or drive

Driving is about 799 miles by road, which we estimate as 1.17 times the straight-line distance. An average car emits about 237 kg of CO2 on the trip, at the EPA figure of 0.297 kg per vehicle-mile. Alone, that's 99% more than the 119 kg for a passenger on the flight.

With 2 people in the car, driving comes out lower per person than the flight (119 kg each, and 59 kg each for four). A larger SUV or pickup (0.394 kg per mile) would emit about 315 kg per vehicle.

CO2 per person, San Francisco 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

Los Angeles to San Francisco75 kg CO2 per passenger over 337 miles Los Angeles to Seattle151 kg CO2 per passenger over 959 miles San Francisco to Las Vegas71 kg CO2 per passenger over 404 miles New York to San Francisco414 kg CO2 per passenger over 2,578 miles New York to Chicago125 kg CO2 per passenger over 730 miles Dallas-Fort Worth to Atlanta127 kg CO2 per passenger over 728 miles Atlanta to Orlando71 kg CO2 per passenger over 404 miles

Airports on this route: Seattle-Tacoma International Airport, San Francisco 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.