Speed is measured using different units.
You can convert the speed measured in one unit to another unit by clicking Utilities and then Conversions.
Holding the Control key and typing q has the same result.
In the Conversions window, select Speed. If you can't see the word Speed
in the Measurement Type box, hit the 
arrow key a few times.
Click the unit you have in the Units From: box, and the units you want in the Units To: box.
Enter the number in the lower left box and click Convert.
This window shows that Mach 1 is 340.3 meters / second.
The conversions are based on:
1 foot / second = 60 feet / minute = 3600 feet / hour
1 meter / second = 60 meters / minute = 3600 meters / hour
1 kilometer / second = 60 kilometers / minute = 3600 kilometers / hour = 1000 meters / second
1 mile / second = 60 miles / minute = 3600 miles / hour = 5280 feet / second
1 mile / hour = 1.609 343 948 5 kilometers / hour
1 knot = 1.852 kilometers / hour
1 knot (UK) = 1.853 184 kilometers / hour
Mach 1 = 340.3 meters / second (at sea level when temperature is 15 Celsius)