1 mph = 1.609344 km/h = 0.44704 m/s = 0.868976 knots = 1.466667 ft/s. 1 knot is one nautical mile per hour, or exactly 1.852 km/h. To convert m/s to km/h, multiply by 3.6.
Example: 100 km/h is 62.14 mph, 27.78 m/s or 53.99 knots.
Knots measure speed at sea and in aviation, and wind speed in weather reports. One knot is about 1.15 mph.
Multiply by 3.6, or roughly by 4 and subtract a little. 10 m/s is 36 km/h.
See also: km/h to mph · Speed Distance Time · Pace