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Rankings / Routes / Los Angeles to Denver

2025 flights

Los Angeles to Denver

Between Los Angeles and Denver, 4.4 million passengers flew nonstop in 2025, on 35 thousand flights of about 850 miles and 1.9 hours in the air. The average passenger accounted for about 130 kg of CO2 from the fuel burned, from 96 kg on Frontier Airlines to 210 kg on SkyWest Airlines.

Los Angeles to Denver is one of the few big routes that grew: passengers rose from 4.1 million in 2019 to 4.4 million, up 9%. The planes didn't fill up with them, though. Seats filled fell from 88% to 78%, so each passenger accounts for 130 kg now against 128 kg then, almost exactly the same.

United and Southwest split the route almost evenly, 42% and 39%, and sit within 4% of each other at 127 and 132 kg. The bigger gaps are at the ends: Frontier at 96 kg on 200-seat Airbus jets, and Delta at 194 kg, because its A319s leave 32% of their seats empty.

  • 130 kgCO2 per passenger, average
  • 850 milesabout 1.9 hours in the air
  • 4.4 millionpassengers in 2025
  • 78%of seats filled

CO2 per passenger, airline by airline

CO2 per passenger by airline, Los Angeles to DenverBar chart of kilograms of CO2 per passenger on each airline between Los Angeles and Denver in 2025.050100150200Frontier Airlines96 kgUnited Airlines127 kgSouthwest Airlines132 kgDelta Air Lines194 kgSkyWest Airlines210 kg
CO2 per passenger by airline, Los Angeles to DenverBar chart of kilograms of CO2 per passenger on each airline between Los Angeles and Denver in 2025.0100200Frontier Airlines96 kgUnited Airlines127 kgSouthwest Airlines132 kgDelta Air Lines194 kgSkyWest Airlines210 kg
Kilograms of CO2 per passenger, one way, 2025. Fuel burned only. Less is better.
Los Angeles to Denver by airline, 2025
AirlineShare of passengersFlights (thousands)Main aircraftSeats per flightSeats filledkg CO2 per passenger
United Airlines42%13.6Boeing 737 MAX 8, Airbus A321neo17180%127
Southwest Airlines39%14.3Boeing 737-700, Boeing 737 MAX 815777%132
Frontier Airlines13%3.5Airbus A320neo, Airbus A321neo20082%96
Delta Air Lines3%1.6Airbus A319, Boeing 737-80013368%194
SkyWest Airlines3%2.4Embraer 1757478%210

What explains the differences

It's number 9 of the 100 busiest city pairs by passengers, and number 52 for the lowest CO2 per mile flown (0.15 kg per passenger-mile, number 1 being the lowest). A typical route of 850 miles in this set comes out at about 133 kg, so this one is close to that.

The flights use more than one pair of airports: DEN to LAX (44%), DEN to SNA (22%), DEN to ONT (17%). The figures here cover all of them.

The airlines on this route differ by 119% per passenger. Frontier Airlines burned 1,613 gallons per flight and 164 passengers on each, and SkyWest Airlines 1,241 gallons and 58 passengers. The gap comes from how many passengers share each flight, not from fuel burned per flight. Frontier Airlines flew 82% full here against 78% for SkyWest Airlines, flying mostly Airbus A320neo against Embraer 175.

For comparison, the EPA default factor for a flight of this length (0.129 kg per passenger-mile) would give 110 kg. The EPA figure is a national average for flights of that length. The measured figure for this route is 18% higher.

2019 compared with 2025

In 2019 the route carried 4.1 million passengers on 30 thousand flights. In 2025 it carried 4.4 million, up 9%, on 35 thousand flights, up 17%. The average flight had 154 seats then and 160 now, and 88% of them were filled against 78%.

CO2 per passenger was 128 kg in 2019 and 130 kg in 2025, up 1.6%. Fuel burned per flight was down 5.9% (1,777 gallons to 1,672) and passengers per flight were down 7.4% (136 to 126). The distance flown was about the same (852 miles then, 850 now).

United Airlines led in both years, with 38% of passengers in 2019 and 42% in 2025. Delta Air Lines lost the most, 7% to 3%. Compass Airlines and Spirit Airlines and American Airlines no longer reach 1% of passengers, having had 6% in 2019.

Airline by airline, Frontier Airlines went from 96 kg to 96 kg per passenger (186 seats per flight to 200, main aircraft Airbus A320neo in both years); Delta Air Lines went from 154 kg to 194 kg per passenger (126 seats per flight to 133, main aircraft Airbus A319 in both years).

The airports changed too: DEN to LAX handled 57% of the passengers in 2019 and 44% in 2025.

Los Angeles to Denver, 2019 and 2025
Measure20192025
Passengers (thousands)4,0854,443
Flights (thousands)30.135.4
Seats filled88%78%
Gallons of fuel per flight1,7771,672
kg CO2 per passenger128130
CO2 per passenger by airline, 2019 and 2025, Los Angeles to DenverBar chart of kilograms of CO2 per passenger on Los Angeles to Denver for each major airline in 2019 and in 2025.050100150200United Airlines 2019126 kgUnited Airlines 2025127 kgSouthwest Airlines 2019126 kgSouthwest Airlines 2025132 kgFrontier Airlines 201996 kgFrontier Airlines 202596 kgDelta Air Lines 2019154 kgDelta Air Lines 2025194 kg
CO2 per passenger by airline, 2019 and 2025, Los Angeles to DenverBar chart of kilograms of CO2 per passenger on Los Angeles to Denver for each major airline in 2019 and in 2025.0100200United Airlines 2019126 kgUnited Airlines 2025127 kgSouthwest Airlines 2019126 kgSouthwest Airlines 2025132 kgFrontier Airlines 201996 kgFrontier Airlines 202596 kgDelta Air Lines 2019154 kgDelta Air Lines 2025194 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.

Los Angeles to Denver and back: time in the air

Flights from Denver to Los Angeles spent 120 minutes in the air on average in 2025, against 111 minutes from Los Angeles to Denver: 9 minutes longer, 8% 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 869 gallons per flight hour, those extra minutes cost about 123 gallons per flight, which is about 1.0 gallons or 10 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
Denver to Los Angeles119.617,723
Los Angeles to Denver111.117,651

Fly or drive

Driving is about 994 miles by road, which we estimate as 1.17 times the straight-line distance. An average car emits about 295 kg of CO2 on the trip, at the EPA figure of 0.297 kg per vehicle-mile. Alone, that's 128% more than the 130 kg for a passenger on the flight.

With 3 people in the car, driving comes out lower per person than the flight (98 kg each, and 74 kg each for four). A larger SUV or pickup (0.394 kg per mile) would emit about 392 kg per vehicle.

CO2 per person by way of travel, Los Angeles to DenverBar chart of kilograms of CO2 per person flying, driving or taking the train between Los Angeles and Denver.0100200300Flight, average130 kgCar, driver alone295 kgCar, 2 people148 kgCar, 4 people74 kg
CO2 per person by way of travel, Los Angeles to DenverBar chart of kilograms of CO2 per person flying, driving or taking the train between Los Angeles and Denver.0100200300Flight, average130 kgCar, driver alone295 kgCar, 2 people148 kgCar, 4 people74 kg
CO2 per person, Los Angeles to Denver. 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.

What to take from it

More than half of the 'Los Angeles' passengers, 56%, use Orange County, Ontario, Burbank or Long Beach rather than LAX. The flight from Denver to Los Angeles takes 9 minutes longer than the one back, 8% more, about 10 kg more per passenger.

SkyWest flies 3% of the route on 74-seat jets at 210 kg, 119% more than Frontier's mainline jets. At 994 miles of road, three people in a car would produce 98 kg each, 24% below the flight.

Routes with shared cities or nearby CO2 per mile

Los Angeles to San Francisco75 kg CO2 per passenger over 337 milesLos Angeles to Las Vegas53 kg CO2 per passenger over 227 milesNew York to Los Angeles406 kg CO2 per passenger over 2,465 milesLos Angeles to Dallas-Fort Worth171 kg CO2 per passenger over 1,222 milesNew York to Tampa153 kg CO2 per passenger over 1,008 milesAtlanta to Boston143 kg CO2 per passenger over 939 milesDenver to Phoenix93 kg CO2 per passenger over 602 milesMiami to Washington, DC144 kg CO2 per passenger over 921 miles

Airports on this route: Denver International Airport, Los Angeles International Airport, John Wayne Airport, Ontario International Airport, Hollywood Burbank 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.