Mach 3 means traveling at three times the speed of sound. At sea level, this corresponds to approximately 2,301 miles per hour (3,705 kilometers per hour)

. However, the exact speed of Mach 3 varies with altitude because the speed of sound decreases as temperature and air density drop at higher elevations. For example, at 30,000 feet, Mach 3 is about 2,156 mph (3,470 kph), and at 50,000 feet, it is closer to 2,021 mph (3,254 kph)

. In summary:

• Mach 3 at sea level ≈ 2,301 mph (3,705 kph)
• Mach 3 at 30,000 feet ≈ 2,156 mph (3,470 kph)
• Mach 3 at 50,000 feet ≈ 2,021 mph (3,254 kph)

This speed is roughly three times the speed of sound at the respective altitude and is achieved by some advanced military aircraft like the SR-71 Blackbird