Concorde's windows were particularly small because it cruised much higher (60,000 feet) than conventional airliners (40,000 feet), and would therefore take longer to descend to survivable outside pressure levels.

The windows on the Concorde were approximately the size of a human hand for critical safety and structural reasons related to its extreme flight profile. Flying at 60,000 feet—nearly twice as high as standard jets—the Concorde operated in a region where the air is too thin to sustain life. If a window were to fail at that altitude, the rate of cabin depressurization would be catastrophic. By keeping the windows small, engineers ensured that even in the event of a breach, the rate of air loss would be slow enough to allow the pilots to perform a rapid emergency descent to a safe altitude before passengers lost consciousness from hypoxia. Structurally, the small windows also minimized the stress on the fuselage; as a pressure vessel, every hole in the airframe requires heavy reinforcement. Given that the Concorde's fuselage was much narrower than modern jets and subjected to intense thermal expansion at Mach 2, smaller windows allowed for a lighter, stronger airframe that could safely handle the high pressure differential between the pressurized cabin and the near-vacuum outside.