Mach number calculator
Mach number from speed and air temperature, with the flight regime named.
Fill in the fields and the result will appear here automatically.
Find speed relative to air divided by local sound speed in an approximate dry-air model. Ground speed cannot automatically replace airspeed when there is wind. M=1 is the sonic boundary;0.8–1.2 is a conventional transonic band.
How it works
Formula and logic
c=331.3√(1+t/273.15) m/s; M=(v/3.6)/c, v in km/h. The model links c to temperature for fixed composition and heat-capacity ratio; the 0.8–1.2 band does not change the mathematical boundary M=1.
Example
At 900 km/h and −50 °C: c≈299.447 m/s,M≈0.8349, within the conventional transonic band. At 20 °C the same 900 km/h gives M≈0.7284. The entered temperature causes the difference; altitude is not another input.
Fields and units
- Speed relative to air — km/h
- Air temperature — °C
How to use
- — Enter speed relative to surrounding air in km/h.
- — Use local air temperature, not vehicle surface temperature.
- — M=0 is allowed; M>1 means supersonic free-stream speed even within the labelled transition band.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- NASA: airspeed and M=1 boundary
- Limitation
- Temperature −80 to 80 °C, nonnegative airspeed and a fixed approximate dry-air model. Surface flow, shocks, humidity and other media are not calculated. The regime label is a broad classification, not aerodynamic analysis.
FAQ
Why does the Mach number depend on temperature?
c=331.3√(1+t/273.15) m/s; M=(v/3.6)/c, v in km/h. The model links c to temperature for fixed composition and heat-capacity ratio; the 0.8–1.2 band does not change the mathematical boundary M=1.
What does the 0.8–1.2 Mach band mean?
Find speed relative to air divided by local sound speed in an approximate dry-air model. Ground speed cannot automatically replace airspeed when there is wind. M=1 is the sonic boundary;0.8–1.2 is a conventional transonic band.
What temperature is there at what altitude?
In the standard atmosphere the temperature falls about 6.5 degrees per kilometre up to eleven kilometres and then holds near −56.5 °C. For an exact figure take the actual temperature from the report.
Does this work for water?
No. Sound travels at about 1500 m/s in water, and the air formula does not apply there. This calculation is meant for air.