Convert Mach, km/h, mph and knots using air temperature or altitude. Mach is the ratio of true airspeed to the local speed of sound, so its speed changes with temperature.
Common Mach conversions at two temperatures
These are true-airspeed conversions in ideal dry air, rounded to one decimal place. They are reference calculations, not measured aircraft speeds. The table stays at the stated temperatures when you change the calculator above.
| Mach | km/h | mph | Knots |
|---|---|---|---|
| 0.8 | 980.0 | 609.0 | 529.2 |
| 1 | 1,225.1 | 761.2 | 661.5 |
| 2 | 2,450.1 | 1,522.4 | 1,323.0 |
| 3 | 3,675.2 | 2,283.6 | 1,984.4 |
| 6.7 | 8,207.8 | 5,100.1 | 4,431.9 |
| 9.6 | 11,760.5 | 7,307.6 | 6,350.2 |
| Mach | km/h | mph | Knots |
|---|---|---|---|
| 0.8 | 849.8 | 528.0 | 458.9 |
| 1 | 1,062.2 | 660.0 | 573.6 |
| 2 | 2,124.5 | 1,320.1 | 1,147.1 |
| 3 | 3,186.7 | 1,980.1 | 1,720.7 |
| 6.7 | 7,117.0 | 4,422.3 | 3,842.9 |
| 9.6 | 10,197.6 | 6,336.5 | 5,506.2 |
Why Mach is not one fixed speed
Mach 1 means travelling at the local speed of sound. In this model, warmer air has a higher sound speed; the same Mach number therefore gives a higher km/h or mph. Use the actual air temperature when it is known, or use the altitude option for a standard-atmosphere comparison.
Formula and model limits
a = √(γRT) speed = Mach × a γ = 1.4; R = 287.05 J/(kg·K); T = °C + 273.15
Dry-air, ideal-gas educational approximation. The altitude option uses 15°C at sea level, a 6.5°C/km lapse rate to 11 km, then −56.5°C to 20 km. It is a simplified standard atmosphere, not local weather. At very high Mach numbers, heating and real-gas effects limit this simple model; this is not a flight-planning calculator.
Try it
Compare Mach 2 at 15°C and −56.5°C. Keep Mach fixed, record both km/h results, and explain what changed. Then open the learning activity for a five-question check.
Sources:NASA Glenn — speed of sound; U.S. Standard Atmosphere, 1976.