The short answer
Commercial aircraft cruise at 36,000 ft (about 10,973 m) because it is where physics, engineering, and weather all line up. The air is thin enough that drag is low, the engines still have enough oxygen to work, and the aircraft sits above most thunderstorms and turbulence. That combination gives the best fuel burn per mile, which is what airlines optimize for.
The “36,000 ft” figure is approximate. Real cruise altitudes range from about FL330 (33,000 ft) to FL410 (41,000 ft) depending on the aircraft type, weight, and route length. Newer composite-airframe aircraft tend to cruise higher than older designs.
This guide unpacks why 36,000 ft, why aviation uses feet at all, and what changes as you climb.
What is at 36,000 ft
At 36,000 ft (10,973 m), the aircraft is in the lower stratosphere of the atmosphere over middle latitudes. The boundary between the troposphere (where weather happens) and the stratosphere is called the tropopause, and it sits at about 36,000 to 39,000 ft over middle latitudes, lower over the poles, higher over the equator. Above the tropopause, the air is dry, stable, and largely free of vertical convection. That is why turbulence is much rarer above 36,000 ft than below.
The air at 36,000 ft is also very thin. Atmospheric pressure is about 23 percent of sea level (227 hPa versus 1013 hPa). The air density is roughly 30 percent of sea level. The outside temperature is approximately minus 56 degrees Celsius (minus 69 degrees Fahrenheit), and remains roughly constant from the tropopause up through the lower stratosphere.
Cabin pressurization keeps the interior of the aircraft at an equivalent altitude of 6,000 to 8,000 ft (about 1,800 to 2,400 m), depending on the aircraft model. The 787 Dreamliner is famous for maintaining a 6,000 ft cabin altitude versus the older 8,000 ft standard, which reduces passenger fatigue on long flights.
The fuel-efficiency case for high cruise
Drag on an aircraft has two parts. Parasitic drag depends on air density (denser air, more drag), and induced drag depends on how hard the wings are working to generate lift (more lift needed, more induced drag). Climbing reduces parasitic drag because the air is thinner, but increases induced drag because the wings have to work harder to stay airborne.
There is an optimal altitude where the sum of these two is minimized. For most commercial aircraft at typical cruise weights, that altitude is between 33,000 and 41,000 ft. Heavier aircraft want lower altitudes (because they cannot afford the higher induced drag of thin air), lighter aircraft want higher altitudes.
The “36,000 ft” round number is the band where a Boeing 737 or Airbus A320 at typical mid-cruise weight is most fuel-efficient. Earlier in a flight, when the aircraft is heavier with fuel, it cruises slightly lower (say FL340). As fuel burns and the aircraft gets lighter, pilots can step-climb to FL360 and then FL380 to stay in the efficiency band. This is called the “step climb” pattern and is visible on flight-tracking sites.
Long-range twin-aisle aircraft like the Boeing 787 and Airbus A350 are designed for higher cruise altitudes. They routinely operate at FL390 to FL410, which is one to two flight levels above the older widebody fleet. The composite materials let them tolerate the slightly higher cabin pressure differential at altitude, and the engines are optimized for thin-air operation.
Above the weather
The second reason 36,000 ft is preferred is that it is above almost all weather. Thunderstorm tops in the United States rarely exceed 50,000 ft and only the most powerful supercells reach above 40,000 ft. Routine convective weather tops out around 35,000 to 40,000 ft. Cruising at FL360 or above keeps the aircraft clear of all but the strongest storms.
The other weather concern is the jet stream. The polar jet stream sits at around 30,000 to 40,000 ft, which is in the cruise band. Flying with the jet stream (eastbound across the North Atlantic, for example) gives a significant tailwind that can shave an hour off a transatlantic flight. Flying against it (westbound) adds fuel burn and time. Routing decisions try to maximize tailwind on eastbound legs and minimize headwind on westbound legs.
Icing is another factor. Below the tropopause, in-cloud icing is a real hazard. Above the tropopause, the air is too cold and too dry for liquid water to exist, so icing is essentially impossible. Cruising at 36,000 ft puts the aircraft in the safest part of the atmosphere from an icing perspective.
Why feet and not metres
The historical reason is that early aviation was dominated by the United States and the United Kingdom, both of which used feet for altitude. Wilbur and Orville Wright, the Wright brothers, recorded their first flight altitude in feet. Every subsequent generation of American and British aircraft used feet, and the rest of the world followed because compatibility with the dominant fleet was more important than unit consistency.
ICAO (the International Civil Aviation Organization) formalized the standard after World War II. Annex 5 to the Chicago Convention designates feet as the primary unit for altitude. The reasoning was practical: too many altimeters, charts, manuals, and training materials already used feet for switching to be cost-effective.
There are a few exceptions. Russia, China, Mongolia, North Korea, and several central Asian states use metres for altitude in their domestic airspace. The Russian metric flight level system uses 300 m increments (FL300m = 300 m × n) that roughly correspond to ICAO 1,000 ft increments. Pilots flying into and out of these countries convert at the border.
The case for switching the world to metres is weak. The system works, the safety record is excellent, and the cost of retraining several million pilots, controllers, and ground crew plus replacing every altimeter and chart is astronomical. ICAO has reviewed the question several times and concluded that the benefit does not justify the cost. Feet will remain the international standard for the foreseeable future.
Common cruise altitudes by aircraft
| Aircraft | Typical cruise | Service ceiling | Metres equivalent (cruise) |
|---|---|---|---|
| Boeing 737-800 | FL360 (36,000 ft) | 41,000 ft | 10,973 m |
| Airbus A320 | FL360-370 | 39,800 ft | 10,973 to 11,278 m |
| Boeing 777-300ER | FL380-410 | 43,100 ft | 11,582 m and up |
| Boeing 787-9 | FL390-410 | 43,100 ft | 11,887 m and up |
| Airbus A350-900 | FL390-410 | 43,100 ft | 11,887 m and up |
| Boeing 747-8 | FL350-380 | 43,100 ft | 10,668 m to 11,582 m |
| Embraer E190 | FL370-410 | 41,000 ft | 11,278 m to 12,497 m |
| Gulfstream G700 | FL450-510 | 51,000 ft | 13,716 m to 15,545 m |
| Cessna Citation X | FL450 | 51,000 ft | 13,716 m |
| Concorde (retired) | FL550-600 | 60,000 ft | 16,764 m to 18,288 m |
For a deeper dive on what flight levels actually mean and why they exist, see our companion guide What are Flight Levels?.
What cruise feels like from inside the cabin
Despite being at 36,000 ft, passengers experience a cabin altitude of 6,000 to 8,000 ft. That is roughly the equivalent of being at the top of a moderate-height mountain, like driving over a high pass in the Rockies or the Alps. Mild fatigue, slightly drier air, and a small drop in oxygen saturation are all normal.
The pressure differential between cabin and outside is enormous: about 8 psi (55 kPa) at 36,000 ft. The aircraft hull is designed to flex slightly under this stress, which is one reason aircraft have a finite “pressurization cycle” lifespan. Each takeoff-cruise-landing cycle counts as one pressurization, and the aircraft is retired or rebuilt after the certified number of cycles.
The view out the window at 36,000 ft is one of the best the atmosphere offers. The horizon is visibly curved (sometimes), the sky is a deeper blue than at sea level, and the cloud tops sit well below the aircraft. On a transcontinental flight, you can sometimes see four states laid out simultaneously.
When 36,000 ft is not the answer
A cruise altitude of 36,000 ft is typical for narrow-body twin-jet aircraft on medium-length routes. It is not optimal for every case.
- Short-hop flights (under 300 nautical miles) often do not climb above FL250-FL300 because the time and fuel spent climbing higher is not recovered before the descent starts.
- Heavy long-range departures with full fuel and a full cabin may start at FL310-FL330 and step-climb later.
- Light private jets are happiest in the FL410-FL510 band and rarely descend to FL360 for cruise.
- Cargo aircraft sometimes operate at lower altitudes (FL280-FL340) because their loading patterns and fuel economics are different from passenger aircraft.
- Helicopters and turboprops operate well below the FL280 floor of jet cruise.
The “36,000 ft” answer is therefore a generalization. The real answer for any specific flight depends on aircraft type, weight, fuel load, route, and weather. What is consistent is that the cruise altitude is always chosen to optimize a clear trade-off between fuel burn, weather avoidance, and traffic constraints. The result for a typical commercial jet on a typical flight just happens to be around 36,000 ft.
Sources and further reading: