Why It's -60°F at 40,000 Feet Above Sea Level

If you've ever wondered what it feels like outside your airplane window during a flight, here's the answer: brutally, bone-chillingly cold. At 40,000 feet—the typical cruising altitude for commercial aircraft—the average temperature hovers around -60 degrees Fahrenheit (or about -51°C). That's colder than most places in Antarctica.

This extreme cold isn't just a quirky atmospheric fact. It's a fundamental reality of how our atmosphere works, and it has massive implications for aviation, weather patterns, and even climate science.

Why Does It Get So Cold Up There?

Temperature drops dramatically as you climb because of decreasing air pressure. At sea level, air molecules are packed tightly together, constantly colliding and generating heat. But as you ascend, air becomes thinner—at 40,000 feet, air density is about one-quarter of what it is at the surface.

The rule of thumb: temperature decreases by roughly 2°C (3.5°F) for every 1,000 feet you climb, up to about 36,000 feet where the tropopause begins. Starting at a comfortable 59°F at sea level, you're looking at a 100°F+ temperature drop by the time you hit cruising altitude.

How Cold Can It Actually Get?

While -60°F is the average, it can get even colder. Depending on weather conditions and latitude, temperatures at 40,000 feet can plunge to -70°F (-57°C) or lower, especially on polar routes between the USA and Europe.

To put this in perspective:

• -60°F is colder than the coldest temperature ever recorded in Alaska (-80°F)
• It's cold enough to instantly freeze exposed skin
• Water turns to ice almost immediately
• Unprotected metal becomes brittle and can shatter

How Do Planes Handle This?

Modern aircraft are engineering marvels designed to function in these extreme conditions. Cabin pressurization keeps passengers comfortable at simulated altitudes of 6,000-8,000 feet, while heating systems maintain cozy interior temperatures. The fuselage acts as a giant insulated thermos, protecting you from the hostile environment just inches away.

Jet engines actually benefit from cold air—denser cold air contains more oxygen, making combustion more efficient. That's one reason airlines prefer high-altitude cruising: better fuel economy and smoother rides above most weather.

Wing and engine de-icing systems prevent ice buildup, while special aviation fuel formulations ensure the kerosene doesn't gel or freeze (jet fuel freezes around -40°F to -58°F, right at the edge of these temperatures).

The Bottom Line

Next time you're on a flight, remember: while you're sipping a lukewarm coffee in your 70°F cabin, the aluminum skin of the plane is being blasted by -60°F winds at 500 mph. It's a testament to human engineering that we've made this frozen, inhospitable environment a routine part of modern travel.

And if you ever hear someone complain about airplane air conditioning being too cold, just remind them it could be 120 degrees colder.