Chicago to Boston

Between Chicago and Boston, 2.7 million passengers flew nonstop in 2025, on 23 thousand flights of about 861 miles and 2.0 hours in the air. The average passenger accounted for about 140 kg of CO2 from the fuel burned, from 122 kg on Southwest Airlines to 216 kg on Envoy Air.

140 kgCO2 per passenger, average
861 milesabout 2.0 hours in the air
2.7 millionpassengers in 2025
85%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 Boston by airline, 2025

Airline	Share of passengers	Flights (thousands)	Main aircraft	Seats per flight	Seats filled	kg CO2 per passenger
United Airlines	29%	5.3	Boeing 737-800, Boeing 737-900ER	172	88%	123
Southwest Airlines	24%	4.8	Boeing 737 MAX 8, Boeing 737-800	165	81%	122
American Airlines	21%	4.0	Boeing 737-800, Airbus A319	163	87%	135
Delta Air Lines	8%	1.9	Airbus A220-300	128	86%	134
Republic Airways	6%	2.4	Embraer 175	76	86%	208
Envoy Air	5%	2.1	Embraer 175	71	86%	216
JetBlue	5%	1.1	Airbus A220-300	133	82%	172
SkyWest Airlines	3%	1.2	Embraer 175	72	86%	201

What explains the differences

It's number 33 of the 100 busiest city pairs by passengers, and number 62 for the lowest CO2 per mile flown (0.16 kg per passenger-mile, number 1 being the lowest). A typical route of 861 miles in this set comes out at about 134 kg, so this one is 4.0% above it.

The flights use more than one pair of airports: BOS to ORD (67%), BOS to MDW (14%), PVD to ORD (8%). The figures here cover all of them.

The airlines on this route differ by 77% per passenger. Southwest Airlines burned 1,667 gallons per flight and 133 passengers on each, and Envoy Air 1,367 gallons and 62 passengers. The gap comes from how many passengers share each flight, not from fuel burned per flight. Southwest Airlines flew 81% full here against 86% for Envoy Air, flying mostly Boeing 737 MAX 8 against Embraer 175.

For comparison, the EPA default factor for a flight of this length (0.129 kg per passenger-mile) would give 111 kg. The EPA figure is a national average for flights of that length. The measured figure for this route is 26% higher.

2019 compared with 2025

In 2019 the route carried 2.9 million passengers on 25 thousand flights. In 2025 it carried 2.7 million, down 7%, on 23 thousand flights, down 10%. The average flight had 135 seats then and 139 now, and 84% of them were filled against 85%.

CO2 per passenger was 147 kg in 2019 and 140 kg in 2025, down 5.0%. Fuel burned per flight was down 1.5% (1,721 gallons to 1,695) and passengers per flight were up 3.7% (114 to 118). The distance flown was about the same (860 miles then, 861 now).

Southwest Airlines had the most passengers in 2019 (27%) and United Airlines in 2025 (29%). Republic Airways gained the most share, 2% to 6%. American Airlines lost the most, 26% to 21%. Delta Air Lines didn't have 1% of the passengers in 2019 and now carries 8%. Spirit Airlines no longer reaches 1% of passengers, having had 2% in 2019.

Airline by airline, JetBlue went from 199 kg to 172 kg per passenger (101 seats per flight to 133, main aircraft Airbus A320-200 then and Airbus A220-300 now); Envoy Air went from 165 kg to 216 kg per passenger (76 seats per flight to 71, main aircraft Embraer 175 in both years).

Chicago to Boston, 2019 and 2025

Measure	2019	2025
Passengers (thousands)	2,891	2,686
Flights (thousands)	25.3	22.7
Seats filled	84%	85%
Gallons of fuel per flight	1,721	1,695
kg CO2 per passenger	147	140

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 Boston and back: time in the air

Flights from Boston to Chicago spent 133 minutes in the air on average in 2025, against 109 minutes from Chicago to Boston: 24 minutes longer, 22% 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 839 gallons per flight hour, those extra minutes cost about 341 gallons per flight, which is about 2.9 gallons or 28 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
Boston to Chicago	133.4	11,332
Chicago to Boston	109.0	11,382

Fly or drive

Driving is about 1,007 miles by road, which we estimate as 1.17 times the straight-line distance. An average car emits about 299 kg of CO2 on the trip, at the EPA figure of 0.297 kg per vehicle-mile. Alone, that's 114% more than the 140 kg for a passenger on the flight.

With 3 people in the car, driving comes out lower per person than the flight (100 kg each, and 75 kg each for four). A larger SUV or pickup (0.394 kg per mile) would emit about 397 kg per vehicle.

CO2 per person, Chicago to Boston. 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

Airports on this route: 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.