2025 flights

Flight CO2 on the busiest US routes

A passenger on a nonstop flight accounts for anything from 39 kg of CO2 (Honolulu to Kahului) to 414 kg (New York to San Francisco) on the 100 busiest US city pairs. These figures use the fuel each airline reported for each type of aircraft, not an average, and each page compares the flight with driving.

A passenger jet wing above a deep blue sea and scattered cloud — Illustrative photo, not a specific airline's aircraft.

The busiest routes

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

What the routes show

Short flights cost more per mile

On routes under 500 miles (20 of the 100), a passenger accounts for a median of 0.24 kg of CO2 per mile. On routes of 1,500 miles or more (16 routes) it's 0.13 kg per mile, 89% less per mile than the short hops. Take-off and climb burn the most fuel, so a short flight is mostly take-off and climb.

The same route, a different airline

The widest gap among airlines on one route is Atlanta to Washington, DC: Spirit Airlines at 71 kg per passenger and PSA Airlines at 214 kg, a gap of 203%. Across every route two or more airlines share, Frontier Airlines came out lowest, at a median of 22% below the route average, and SkyWest Airlines highest, at 48% above it.

Airlines compared on the same routes

Airline	Routes	Median against the route average
Frontier Airlines	74	-22%
Spirit Airlines	56	-20%
Alaska Airlines	19	-8%
Southwest Airlines	82	-2%
United Airlines	70	+1%
American Airlines	57	+4%
Delta Air Lines	54	+6%
JetBlue	27	+9%
Republic Airways	16	+36%
Envoy Air	10	+48%
SkyWest Airlines	22	+48%

Why flights west take longer

On the 24 routes that run at least 20 degrees of longitude east to west (roughly 1,000 miles or more) and have flying both ways, the westbound flight spends a median of 28 minutes more in the air than the eastbound one, 14% longer. The gap is the winds: aircraft flying west meet the prevailing west-to-east winds head on. The biggest differences among the 100 routes with at least 200 flights each way are below. Extra minutes in the air are extra fuel, which is why the per passenger figures on each route page average both directions.

The routes with the biggest difference between directions

Route	Slower direction	Minutes	Faster way	Difference
Chicago to Boston	Boston to Chicago	133	109	24 min, 22%
Denver to Washington, DC	Washington, DC to Denver	208	172	36 min, 21%
Washington, DC to Boston	Boston to Washington, DC	74	62	12 min, 20%
New York to Denver	New York to Denver	228	191	37 min, 19%
Atlanta to Denver	Atlanta to Denver	172	144	28 min, 19%
New York to Chicago	New York to Chicago	117	98	18 min, 19%
New York to Boston	Boston to New York	48	41	8 min, 18%
Chicago to Philadelphia	Philadelphia to Chicago	106	90	16 min, 18%

Flying or driving

Driving alone in an average car emits about 0.30 kg of CO2 per mile, so on a 600 mile trip a driver on their own produces about 208 kg against about 102 kg for a passenger on a typical flight of that length. Split between two people, the car is clearly lower. The flying vs driving guide works through trip lengths from 200 to 2,500 miles, with the train. A second guide compares a private jet with an airline seat.

All 100 routes

Every route, busiest first

Route	Miles	Passengers (millions)	kg CO2 per passenger	kg per mile	Lowest airline
Los Angeles to San Francisco	337	8.9	75	0.22	Frontier Airlines
New York to Miami	1,082	8.7	158	0.15	Frontier Airlines
New York to Orlando	947	5.7	141	0.15	Frontier Airlines
New York to Chicago	730	5.7	125	0.17	Spirit Airlines
New York to Atlanta	758	5.5	124	0.16	Frontier Airlines
Los Angeles to Las Vegas	227	5.3	53	0.23	Frontier Airlines
New York to Los Angeles	2,465	5.2	406	0.16	Frontier Airlines
Los Angeles to Dallas-Fort Worth	1,222	4.7	171	0.14	Frontier Airlines
Los Angeles to Denver	850	4.4	130	0.15	Frontier Airlines
Los Angeles to Phoenix	354	4.3	74	0.21	Frontier Airlines
Washington, DC to Boston	383	4.1	100	0.26	Spirit Airlines
Atlanta to Miami	587	4.1	96	0.16	Spirit Airlines
Atlanta to Washington, DC	554	3.9	104	0.19	Spirit Airlines
Los Angeles to Seattle	959	3.7	151	0.16	Frontier Airlines
San Francisco to Las Vegas	404	3.7	71	0.18	Frontier Airlines
Los Angeles to Chicago	1,739	3.7	225	0.13	Frontier Airlines
New York to San Francisco	2,578	3.6	414	0.16	Alaska Airlines
New York to Dallas-Fort Worth	1,384	3.6	203	0.15	Frontier Airlines
San Francisco to San Diego	436	3.5	78	0.18	Frontier Airlines
Miami to Washington, DC	921	3.5	144	0.16	Spirit Airlines
Chicago to Washington, DC	609	3.3	121	0.20	Frontier Airlines
San Francisco to Seattle	683	3.1	119	0.17	Alaska Airlines
Washington, DC to Orlando	770	3.0	124	0.16	Frontier Airlines
New York to West Palm Beach	1,035	3.0	166	0.16	Frontier Airlines
San Francisco to Denver	960	2.9	136	0.14	Frontier Airlines
New York to Charlotte	541	2.9	117	0.22	Spirit Airlines
Chicago to Denver	890	2.8	129	0.14	Frontier Airlines
Dallas-Fort Worth to Washington, DC	1,193	2.7	178	0.15	Frontier Airlines
Chicago to Dallas-Fort Worth	800	2.7	126	0.16	Frontier Airlines
New York to Denver	1,616	2.7	213	0.13	Frontier Airlines
Atlanta to Orlando	404	2.7	71	0.18	Frontier Airlines
Chicago to Miami	1,187	2.7	161	0.14	Spirit Airlines
Chicago to Boston	861	2.7	140	0.16	Southwest Airlines
Los Angeles to Houston	1,373	2.7	183	0.13	Frontier Airlines
New York to Houston	1,412	2.7	197	0.14	Spirit Airlines
Los Angeles to Honolulu	2,560	2.7	321	0.13	Southwest Airlines
Dallas-Fort Worth to Miami	1,119	2.6	160	0.14	Frontier Airlines
Chicago to Orlando	1,000	2.6	137	0.14	Spirit Airlines
Los Angeles to Atlanta	1,937	2.6	261	0.13	Frontier Airlines
Los Angeles to Sacramento	379	2.6	92	0.24	Frontier Airlines
Dallas-Fort Worth to Atlanta	728	2.6	127	0.17	Frontier Airlines
New York to Tampa	1,008	2.5	153	0.15	Frontier Airlines
Denver to Washington, DC	1,471	2.5	192	0.13	Frontier Airlines
Dallas-Fort Worth to Denver	644	2.5	102	0.16	Frontier Airlines
Dallas-Fort Worth to Las Vegas	1,059	2.5	148	0.14	Frontier Airlines
Chicago to Phoenix	1,441	2.4	190	0.13	Frontier Airlines
San Francisco to Phoenix	641	2.4	107	0.17	Frontier Airlines
Chicago to Atlanta	601	2.4	107	0.18	Spirit Airlines
Denver to Phoenix	602	2.4	93	0.15	Frontier Airlines
Chicago to San Francisco	1,845	2.4	235	0.13	Alaska Airlines
New York to Boston	187	2.4	76	0.41	United Airlines
Dallas-Fort Worth to Phoenix	872	2.4	127	0.15	Frontier Airlines
Dallas-Fort Worth to Houston	233	2.4	67	0.29	Southwest Airlines
Chicago to Las Vegas	1,516	2.3	194	0.13	Spirit Airlines
Dallas-Fort Worth to Orlando	981	2.3	138	0.14	Frontier Airlines
Denver to Houston	869	2.2	119	0.14	Frontier Airlines
Miami to Boston	1,244	2.2	186	0.15	Spirit Airlines
Chicago to Houston	928	2.2	134	0.14	Spirit Airlines
Los Angeles to Salt Lake City	583	2.2	106	0.18	Frontier Airlines
Orlando to Boston	1,111	2.1	163	0.15	Frontier Airlines
New York to San Juan	1,603	2.1	202	0.13	Frontier Airlines
New York to Washington, DC	215	2.1	86	0.40	United Airlines
Miami to Charlotte	642	2.1	109	0.17	Spirit Airlines
Atlanta to Houston	692	2.1	116	0.17	Frontier Airlines
Washington, DC to Houston	1,216	2.0	193	0.16	Spirit Airlines
Honolulu to Kahului	100	2.0	39	0.39	Southwest Airlines
Miami to Houston	964	2.0	142	0.15	Spirit Airlines
New York to Las Vegas	2,239	2.0	284	0.13	Frontier Airlines
New York to Detroit	499	2.0	106	0.21	Spirit Airlines
Denver to Las Vegas	628	2.0	91	0.15	Frontier Airlines
Orlando to San Juan	1,189	2.0	138	0.12	Frontier Airlines
Dallas-Fort Worth to San Francisco	1,458	2.0	193	0.13	Frontier Airlines
Atlanta to Tampa	406	2.0	73	0.18	Frontier Airlines
Los Angeles to Portland	837	1.9	138	0.17	Frontier Airlines
Los Angeles to Washington, DC	2,306	1.9	290	0.13	Spirit Airlines
Denver to Salt Lake City	391	1.8	73	0.19	Frontier Airlines
Seattle to Phoenix	1,107	1.8	164	0.15	Frontier Airlines
Atlanta to Boston	939	1.8	143	0.15	Spirit Airlines
Denver to Seattle	1,024	1.8	135	0.13	Frontier Airlines
New York to Raleigh-Durham	427	1.8	102	0.24	Frontier Airlines
Chicago to Minneapolis	338	1.8	82	0.24	Sun Country Airlines
Miami to Philadelphia	1,003	1.8	152	0.15	Frontier Airlines
Seattle to Anchorage	1,448	1.8	203	0.14	Alaska Airlines
Chicago to Seattle	1,722	1.8	220	0.13	Alaska Airlines
San Francisco to Honolulu	2,404	1.8	300	0.12	Southwest Airlines
San Francisco to Portland	554	1.7	103	0.19	Alaska Airlines
Denver to Minneapolis	680	1.7	101	0.15	Frontier Airlines
Washington, DC to Charlotte	339	1.7	82	0.24	Frontier Airlines
Orlando to Philadelphia	861	1.7	118	0.14	Frontier Airlines
Atlanta to Denver	1,199	1.7	165	0.14	Frontier Airlines
Dallas-Fort Worth to Seattle	1,660	1.7	211	0.13	Southwest Airlines
Las Vegas to Seattle	867	1.7	128	0.15	Frontier Airlines
Los Angeles to Miami	2,342	1.6	292	0.12	Spirit Airlines
Orlando to Houston	852	1.6	117	0.14	Frontier Airlines
Dallas-Fort Worth to San Antonio	247	1.6	60	0.24	American Airlines
Chicago to Philadelphia	675	1.6	112	0.17	Frontier Airlines
New York to Nashville	761	1.6	150	0.20	Spirit Airlines
Atlanta to Las Vegas	1,747	1.6	229	0.13	Frontier Airlines
Las Vegas to Houston	1,227	1.6	164	0.13	Frontier Airlines
Dallas-Fort Worth to Austin	190	1.6	51	0.27	American Airlines

How we worked it out. For each airline and aircraft type on a pair of cities we took flights, seats, passengers and time in the air from BTS T-100 data and multiplied the air time by the gallons per airborne hour the airline reported for that type (BTS Schedule T-2). Flights are listed under the airline that operates them, so regional flying appears under the regional airline. Cities are BTS city markets, so New York means Newark, JFK and LaGuardia together, and the pairs cover domestic flights only. The 100 pairs are the busiest by passengers in 2025. Only CO2 from burning fuel is counted. See the methodology.