Mach Number Calculator
Convert between true airspeed and Mach for the local temperature.
How this is calculated
How it works
M = TAS ÷ a, where a = 38.97 × √(OAT K) is the local speed of sound. Nothing else enters: not pressure, not altitude directly — altitude matters only through the temperature it brings.
The practical consequence
Jets climb at an indicated airspeed and then hold a Mach for exactly this reason: as the air cools with altitude the same IAS creeps toward the critical Mach, so at the changeover altitude the crew stops flying airspeed and starts flying Mach. Run 300 kt TAS at −20 °C and again at −56 °C above to watch the Mach change with no speed change at all.
Live: the coldest air aloft over the US
Cold air lowers the local speed of sound, so the same TAS is a higher Mach. These are the levels and stations where that effect is strongest right now — across the US only, since the FB forecast this comes from is an FAA product.
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For planning and study, not for operational use. Aircraft performance comes from your POH, not from a generic formula.