Enter an object's speed and the medium (or temperature) to calculate its Mach number — the ratio of object speed to the speed of sound. Choose your preferred speed unit (m/s, km/h, knots, or mph) and get back the Mach number, the speed of sound in the selected conditions, and the flow regime (subsonic, transonic, supersonic, or hypersonic). Also try the Friction Loss Calculator.
Mach Number
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Speed of Sound
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Object Speed
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Flow Regime
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The Mach number is a dimensionless quantity that represents the ratio of the speed of an object to the speed of sound in the surrounding medium. It is named after Austrian physicist Ernst Mach. A Mach number of 1 means the object is traveling exactly at the speed of sound. See also our Surface Tension (γ) — Surface Tension.
Mach number (M) is calculated using the formula M = v / c, where v is the speed of the object and c is the speed of sound in the medium. For air at 20°C, the speed of sound is approximately 343 m/s. Simply divide the object's speed by this value to get the Mach number.
Subsonic flow occurs when the Mach number is less than 1 (M < 1), meaning the object travels slower than the speed of sound. Supersonic flow is when M > 1, meaning faster than sound. Transonic flow is the range around M = 0.8–1.2, and hypersonic flow is generally M > 5. These regimes have very different aerodynamic properties.
Yes. In air, the speed of sound increases with temperature. At 0°C it is about 331 m/s, and at 20°C it is about 343 m/s. The relationship follows c = 331.3 × √(1 + T/273.15) m/s, where T is temperature in Celsius. This is why aircraft at high altitude (cold air) need less speed to reach a given Mach number. You might also find our calculate Archimedes' Principle Buoyant Force (F_B) useful.
Most commercial aircraft cruise at around Mach 0.78–0.85, which is just below the speed of sound. Concorde, the retired supersonic passenger jet, cruised at around Mach 2.04. Military fighter jets can reach Mach 2 or higher.
The critical Mach number is the speed at which airflow over some part of the aircraft (usually the wings) first reaches supersonic speed, even if the aircraft itself is still subsonic. Exceeding it can cause shock waves, buffeting, loss of lift, and control difficulties — a phenomenon historically called 'compressibility effects' or 'Mach tuck'.
The ISS orbits Earth at approximately 7,660 m/s. At its orbital altitude (~400 km), the atmosphere is extremely thin and temperature very low, putting the speed of sound around 270–300 m/s. This gives the ISS a Mach number of roughly Mach 25, well into the hypersonic range.
The speed of light is approximately 299,792,458 m/s. Dividing by the speed of sound in air (≈343 m/s) gives roughly Mach 874,030. The concept of Mach number is typically used for objects moving through a fluid medium and is not physically meaningful at relativistic speeds.