Mach Number CalculatorFree online other calculator — instant results, no sign-up
Calculate Mach number using a specified local speed of sound.
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About the Mach Number Calculator
The Mach Number Calculator divides an object's speed by a specified local speed of sound to show how fast it travels relative to sound in that medium. You enter both speeds in m/s, so the tool uses your local sound-speed value rather than assuming a fixed atmospheric condition. With the default inputs of 250 m/s and 343 m/s, the Mach number is 0.728863.
- Object speed (m/s)
- The object's speed relative to the surrounding medium, measured in meters per second (m/s), with a default of 250.
- Local sound speed (m/s)
- The speed at which sound travels through the surrounding medium under local conditions, measured in meters per second (m/s), with a default of 343.
Formula and method
M = v / a; with the default inputs, M = 250 / 343 ≈ 0.728863.
- MMach number, a dimensionless ratio of object speed to local sound speed.
- vObject speed relative to the surrounding medium, in m/s.
- aLocal speed of sound in the surrounding medium, in m/s.
Divide the object speed by the local sound speed. Because both inputs use m/s, their units cancel, leaving a dimensionless Mach number. For the default inputs, dividing 250 by 343 and rounding to six decimal places gives 0.728863.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Object speed250 m/s
- Local sound speed343 m/s
Results
- Result0.728863
How to use the Mach Number Calculator
- 1Enter the object's speed relative to the surrounding medium in Object speed (m/s); the default is 250.
- 2Enter the local speed of sound in Local sound speed (m/s); the default is 343.
- 3Check that the object speed is nonnegative and the local sound speed is greater than zero.
- 4Run the calculation to divide object speed by local sound speed.
- 5Read the Mach number result: the default inputs produce 0.728863, which is below the local speed of sound.
Reading your result
The Result row reports the dimensionless Mach number. The default result of 0.728863 means the object travels at approximately 72.8863% of the specified local speed of sound. A Mach number below 1 indicates subsonic speed, 1 indicates sonic speed, and above 1 indicates supersonic speed; speeds near 1 are commonly described as transonic.
Limitations
This calculator assumes both speeds describe the same local medium and conditions. Object speed must be measured relative to that medium, so ground speed may not be suitable when wind or currents are present. The tool does not derive sound speed from temperature, composition, or other environmental properties; 343 m/s is a default, not a universal constant. Local sound speed must be positive, and object speed must be nonnegative. The result alone does not predict shock waves, drag, heating, or other flow effects, and six displayed decimal places do not imply that the inputs are equally precise.
Common questions
Why does 250 m/s give a Mach number of 0.728863?+
Using the specified local sound speed of 343 m/s, the calculator divides 250 by 343. Rounded to six decimal places, this is 0.728863, so the object is traveling below the local speed of sound.
Should I keep the default local sound speed of 343 m/s?+
Use it only if it reasonably represents your local conditions. It is approximately the speed of sound in dry air near 20°C; other temperatures, gas compositions, or media require an appropriate sound-speed value.
Should I enter an aircraft's airspeed or ground speed?+
Enter its true airspeed relative to the surrounding air, not its ground speed or uncorrected indicated airspeed. Wind can change ground speed without changing the aircraft's Mach number relative to the air.
Can this calculator calculate Mach number in water or another medium?+
Yes, provided you supply the local sound speed for that medium and the object's speed relative to it, both in m/s. The default sound speed of 343 m/s should not be assumed suitable for water or other media.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
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Results are estimates for informational purposes and are not financial, medical or legal advice.