Mach Number Calculator
Mach, regime, and sound speed from airspeed.
What it does
Mach numbers pace flight against sound itself: 450 knots at minus 55 reads 0.782 because cold air slows sound to 576. Heat reverses the trade on runways.
The tool above takes true airspeed with outside temperature in knots or km/h. It returns Mach with regime and sound speed.
The default 450 kts at minus 55 gives Mach 0.782 subsonic. The 300 kts at 15 C case gives 0.454, and metric 830 km/h mirrors the cruise band.
Training handbooks define Mach from true speed over temperature driven sound speed. Safety knowledge repeats the subsonic and transonic bands beside it.
Regimes rule handling: drag spikes near 1 while manuals cap each airframe. Plan with Mach, fly by the book, and respect temperature swings.
How to use
- Pick knots or km/h.
- Type true airspeed.
- Type OAT in C.
- Read Mach first.
- Read regime beside it.
- Read sound speed last.
Formula
- TAS
- True airspeed in kts.
- OAT
- Outside air temp in Celsius.
- a
- Local sound speed in kts.
Aviation training handbooks define Mach from true airspeed over local sound speed with temperature driven sound values. Aviation safety knowledge mirrors the same subsonic and transonic bands. Metric inputs convert km/h at 1.852 first.
Worked example
Example: airliner cruise
Imperial defaults: 450 kts, minus 55 C.
- Jet: 450 kts true at minus 55 C.
- Sound: 38.97 x root(218.15) = 576 kts.
- Mach: 450 / 576 = 0.782.
- Regime: under 0.8 reads subsonic.
- Metric: 830 km/h mirrors the same band.
- Tool shows Mach 0.782, Subsonic, 576 kts.
Reference table
| Mach | Regime | Note |
|---|---|---|
| Under 0.8 | Subsonic | Airliners cruise |
| 0.8 to 1.2 | Transonic | Drag spike |
| Over 1.2 | Supersonic | Fighters plus |
| 1.0 | Sonic | Boom carpet |
Common mistakes
Try it yourself
Quick checks. Answers sit tucked under each question.
300 kts at 15 C?
Mach 0.454 subsonic with sound at 662 kts.
830 km/h at minus 55?
Mach 0.779 subsonic, mirroring cruise.
5000 kts?
Past 2000 kts exceeds entry bounds: check units first.
Questions
Mach math?
True speed over local sound speed: 38.97 times root of Kelvin temp in knots.
Regimes?
Under 0.8 subsonic, 0.8 to 1.2 transonic, above supersonic. Drag spikes near 1.
Temperature effects?
Yes, cold air slows sound, raising Mach at fixed speed. Hot runways reverse it.
Any airspeed?
No, indicated and calibrated speeds correct for instruments first. This page takes true.
Humidity?
Yes, humidity trims slightly. Dry math rules planning here.
Fly by math?
No, this plans Mach bands. Flight manuals rule limits, never arithmetic.