Mach from CAS & Altitude Calculator
What Mach does a given calibrated airspeed produce at altitude? The exact subsonic pitot inversion every air-data computer performs.
Notice temperature appears nowhere: Mach from CAS and pressure altitude is temperature-independent โ both are pressure measurements. Temperature only enters when you want TAS out of the Mach.
Formula
โ ๏ธ For flight planning and education only โ verify with your POH/AFM, certified instruments and official sources. Not for primary navigation or airworthiness decisions.
What Mach does a given calibrated airspeed produce at altitude? The exact subsonic pitot inversion every air-data computer performs.
About Mach from CAS & Altitude Calculator
Inside every air-data computer, Mach is born from two pressures: the pitot's impact pressure against the static port's ambient. This calculator replicates that exact computation โ CAS to impact-pressure ratio, divided by the altitude's pressure ratio, inverted through the subsonic compressible-flow law to Mach. The instructive surprise it makes visible: temperature never enters; Mach from CAS and pressure altitude is a temperature-free fact.
How to use Mach from CAS & Altitude Calculator
- 1Enter โ sensible defaults are pre-filled so you see a worked result immediately.
- 2Read the live results: .
- 3Check the "With your numbers" line to see the formula M = โ(5[((qc/p)+1)^{2/7} โ 1]); qc/p = [(1+0.2(CAS/aโ)ยฒ)^3.5 โ 1]/ฮด substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use Mach from CAS & Altitude Calculator?
- โInstant, free and private โ every calculation runs in your browser, nothing is uploaded
- โBuilt on the published formula M = โ(5[((qc/p)+1)^{2/7} โ 1]); qc/p = [(1+0.2(CAS/aโ)ยฒ)^3.5 โ 1]/ฮด with sources cited on the page
- โNotice temperature appears nowhere: Mach from CAS and pressure altitude is temperature-independent โ both are pressure measurements. Temperature only enters when you want TAS out of the Mach.
- โSwitch units, tweak any input and watch every result update live
Frequently asked questions
Why doesn't temperature appear in the CAS-to-Mach computation?+
Both CAS and pressure altitude are pure pressure measurements, and Mach is itself definable as a function of the impact-to-static pressure ratio alone (the compressible Bernoulli relation). Temperature only matters when converting Mach onward to TAS โ which is why a Machmeter needs no temperature probe but a TAS readout does.
What Mach is 300 KCAS at FL310?+
About M0.80 โ right at many single-aisles' MMO neighborhood, which is why you won't see that combination flown; the schedule caps at the Mach first. Try 280 KCAS at the same level (M0.745) to see a realistic climb condition. The crossover-altitude tool finds where any pair meets exactly.
Is this formula valid at any speed?+
Up to Mach 1 at the pitot. The 3.5-power subsonic relation assumes shock-free flow into the tube; above M1.0 a bow shock forms ahead of the pitot and the Rayleigh supersonic pitot formula takes over. For all airliner and GA operations the subsonic law used here is exact.
How do MMO and VMO interact through this math?+
VMO (a CAS) and MMO (a Mach) are both plotted on the same airspeed tape by the ADC using exactly this conversion: below crossover VMO is the lower true limit, above it MMO converts to an ever-smaller CAS โ the 'barber pole' creeping down as you climb. This tool computes the pole's position by hand.
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