Mach to MPH Converter

Multiply the Mach number by the local speed of sound, then convert that speed to miles per hour. The speed of sound depends on air temperature: a = sqrt(1.4 * 287.05287 * T), where T is the absolute temperature in kelvin. At a standard sea level day (15 C) the speed of sound is about 761 mph, so Mach 2 is roughly 1,522 mph there.

Both figures are correct for different air temperatures. Mach 1 is about 761 mph at the ISA standard sea level temperature of 15 C (59 F), and about 768 mph at a 20 C (68 F) room-temperature day. Since the speed of sound rises with temperature, warmer air makes Mach 1 a faster mph value.

Yes, but only through temperature, not pressure or altitude directly. Air gets colder as you climb to the jet cruise range, so the speed of sound drops to roughly 660 mph near the tropopause (around -56.5 C). That is why an airliner cruising at Mach 0.85 covers fewer mph at altitude than the same Mach number would at sea level. Use the cruise altitude preset or enter the actual outside air temperature for an accurate answer.

Switch the converter to mph to Mach, then enter your speed in miles per hour. The tool divides your speed by the speed of sound at the chosen temperature. For example, 1,000 mph at a standard sea level day (15 C) works out to about Mach 1.31.

It models dry air as an ideal gas with a ratio of specific heats (gamma) of 1.4 and a specific gas constant of 287.05287 J per kg per kelvin, matching the ISA standard atmosphere. Humidity, very high speeds where air chemistry changes, and non-standard gas mixtures are not modeled, so treat results in extreme conditions as approximate.