The regulations^2,3 stipulate that the maximum cabin altitude should not exceed 8000 feet during normal operations, and, in fact, at usual cruising altitude the cabin altitude rarely exceeds 6000 or 7000 feet in a modern jet airliner.

When a commercial jet is cruising at 35,000 to 40,000 feet, the "cabin altitude"—the equivalent atmospheric pressure inside the plane—is typically maintained between 6,000 and 8,000 feet. This means that although you are nearly 7 miles high, your body feels as if it is standing on top of a mountain like Mexico City or Aspen, Colorado. The reason for this is structural; if the cabin were pressurized to sea level (0 feet), the pressure difference between the inside and the "thin" outside air would put immense stress on the aircraft's hull, eventually causing metal fatigue. In 2026, newer composite aircraft like the Boeing 787 Dreamliner and the Airbus A350 are able to maintain a lower cabin altitude of approximately 6,000 feet because their carbon-fiber hulls are much stronger and more resistant to expansion than traditional aluminum. This lower altitude significantly reduces "jet lag" symptoms, headaches, and fatigue, as the blood can carry more oxygen. For passengers, the higher the "cabin altitude," the drier the air and the more likely you are to feel dehydrated, which is why drinking water and using moisturizer are staple tips for long-haul travel.