Mach Converter
Convert between Mach number and everyday speed units. The speed of sound changes with temperature, so you can set the air temperature too.
How to use the Mach Converter
- Enter a speed or Mach number.
- Choose the unit.
- Adjust the air temperature if needed (15 °C is sea-level standard).
How it works
Mach number is speed divided by the local speed of sound. The speed of sound in dry air is approximately a = 331.3 × √(1 + T/273.15) m/s, where T is in °C — about 340 m/s (761 mph) at 15 °C. At airliner cruising altitudes the air is around −56 °C, so Mach 1 is only about 660 mph there.
Mach at sea level (15 °C)
| Mach | mph | km/h | Knots |
|---|---|---|---|
| 0.5 | 381 | 612 | 331 |
| 0.8 | 609 | 980 | 529 |
| 0.85 | 647 | 1,041 | 562 |
| 1 | 761 | 1,225 | 661 |
| 1.5 | 1,142 | 1,837 | 992 |
| 2 | 1,522 | 2,450 | 1,323 |
| 3 | 2,284 | 3,675 | 1,984 |
| 5 | 3,806 | 6,125 | 3,307 |
Frequently asked questions
How fast is Mach 1 in mph?
About 761 mph at sea level at 15 °C; about 660 mph at 35,000 ft.
How fast do airliners fly?
Around Mach 0.78–0.85, roughly 560–600 mph at cruise altitude.
What is hypersonic?
Speeds above Mach 5.
Does the speed of sound depend on altitude?
It depends on temperature, which usually falls with altitude.