Convert speed instantly, with the working shown.
Speed is distance over time, so every conversion combines a distance factor and a time factor. The most useful one to know is that dividing km/h by 3.6 gives metres per second, and multiplying by 3.6 reverses it — the 3.6 comes from 1,000 metres divided by 3,600 seconds. Between km/h and mph the factor is 1.609, the same as the mile-to-kilometre conversion, since the time unit is identical on both sides.
Two other units appear in specific fields. The knot is one nautical mile per hour, about 1.852 km/h, used in aviation and at sea because a nautical mile corresponds to one minute of latitude, which makes navigation arithmetic straightforward. Mach number is not a fixed speed at all but a ratio to the local speed of sound, which falls as air gets colder — so Mach 1 at cruising altitude is a slower true airspeed than Mach 1 at sea level. That is why aircraft speeds are quoted in Mach rather than a fixed figure.
Divide by 3.6, and multiply by 3.6 to convert back. The factor is 1,000 metres divided by 3,600 seconds, so 90 km/h is 25 m/s.
One nautical mile per hour, about 1.852 km/h. It is used in aviation and at sea because a nautical mile equals one minute of latitude, which simplifies navigation calculations.
No. Mach is a ratio to the local speed of sound, which decreases as air temperature falls. Mach 1 at high altitude is a lower true airspeed than Mach 1 at sea level.
1.609, the same as the mile-to-kilometre conversion, because the time unit is the same on both sides. So 60 mph is about 96.6 km/h.