Speed Conversion
Convert between speed units including m/s, km/h, mph, knots, Mach, and the speed of light with step-by-step solutions.
Speed Conversion
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Formula: converted = value x (fromFactor / toFactor)
Worked example — 120 km/h = 33.3333 m/s = 74.5645 mph
Formula
converted = value x (fromFactor / toFactor)
Speed conversion works by multiplying the input value by the ratio of conversion factors. Each unit has a known factor that converts it to meters per second. The result is obtained by converting the input to m/s, then from m/s to the target unit.
Worked Examples
Example 1: Highway Speed Conversion
Problem:Convert 120 km/h to mph and m/s.
Solution:120 km/h to m/s: 120 / 3.6 = 33.3333 m/s 120 km/h to mph: 33.3333 / 0.44704 = 74.5645 mph
Result:120 km/h = 33.3333 m/s = 74.5645 mph
Example 2: Jet Speed in Knots
Problem:A jet flies at Mach 0.85. Convert to knots.
Solution:Mach 0.85 to m/s: 0.85 x 343 = 291.55 m/s m/s to knots: 291.55 / 0.514444 = 566.66 knots
Result:Mach 0.85 = 566.66 knots
Frequently Asked Questions
How do you convert between speed units?
Speed conversion works by first converting the input value to a base unit (meters per second), then converting from that base unit to the desired output unit. Each unit has a known conversion factor relative to m/s. For example, 1 km/h equals 1/3.6 m/s, and 1 mph equals 0.44704 m/s. This two-step process ensures accurate conversion between any pair of speed units.
What is the difference between speed and velocity?
Speed is a scalar quantity that measures how fast an object is moving regardless of direction, while velocity is a vector quantity that includes both magnitude and direction. For instance, a car traveling at 60 km/h has a speed, but a car traveling at 60 km/h northward has a velocity. In everyday use and unit conversion, the terms are often used interchangeably since we are concerned with magnitude.
What is Mach number and how fast is it?
Mach number is the ratio of an objects speed to the speed of sound in the surrounding medium. At sea level and standard conditions, Mach 1 is approximately 343 meters per second or about 1,235 km/h. Mach 2 is twice the speed of sound. Aircraft like the Concorde flew at Mach 2.04, while modern fighter jets can exceed Mach 2.5.
How fast is the speed of light?
The speed of light in a vacuum is exactly 299,792,458 meters per second, which is approximately 1.08 billion km/h or about 670.6 million mph. This is the fastest speed possible according to Einstein's theory of special relativity. Light can travel around the Earth approximately 7.5 times in one second at this speed.
Why are knots used in aviation and marine navigation?
Knots are used in aviation and marine navigation because they are directly tied to the geographic coordinate system. One knot equals one nautical mile per hour, and one nautical mile corresponds to one minute of latitude on the Earth's surface. This makes distance and speed calculations on navigational charts straightforward, which is why knots have remained the standard unit in these fields for centuries.
How do I convert kilometres per hour to miles per hour in my head?
One mile is exactly 1.609344 kilometres, so mph = km/h divided by 1.609344, or km/h multiplied by 0.621371. A quick mental shortcut is to take 60 percent of the km/h figure and add a little: 80 km/h is roughly 48 plus a bit, and the exact answer is 49.7 mph. Going the other way, multiply mph by 1.6 for a close estimate, so a 70 mph motorway limit is about 112 km/h.
What is the difference between airspeed and ground speed in aviation?
Airspeed measures an aircraft speed relative to the surrounding air mass, while ground speed measures its speed relative to the terrain below. The two differ by the wind component along the flight path: a 450 knot true airspeed with a 50 knot tailwind gives 500 knots over the ground, and the same aircraft into a 50 knot headwind makes only 400 knots. Airspeed drives aerodynamic behaviour and stall margins, while ground speed drives flight time and fuel planning.
How is running pace related to speed, and how do I convert between them?
Pace is the reciprocal of speed, expressed as time per unit distance rather than distance per unit time. To turn km/h into minutes per kilometre, divide 60 by the speed: 12 km/h becomes 60 divided by 12, or 5:00 per km. To turn a pace back into speed, divide 60 by the pace in minutes, so a 6:00 per km pace equals 10 km/h. Because the relationship is reciprocal rather than proportional, a given pace improvement at fast speeds represents a much larger speed gain than the same improvement at slow speeds.
Why does the speed of sound change with altitude and temperature?
In an ideal gas the speed of sound depends on the absolute temperature of the medium, not on pressure or altitude directly, and it rises with the square root of temperature in kelvin. That is why sound travels at roughly 340 m/s in 15 degree Celsius sea level air but noticeably slower in the cold air of the upper troposphere. This matters for Mach number, which is a ratio to the local speed of sound: an aircraft holding a fixed true airspeed climbs into colder air and its Mach number rises even though its speed in m/s has not changed.
What is the difference between feet per second and miles per hour?
Both measure speed, but the foot per second is the customary unit for short distance and short duration work such as ballistics, projectile motion and traffic reconstruction, while miles per hour is the road and everyday unit. Because a mile is 5,280 feet and an hour is 3,600 seconds, 1 mph equals 5280 divided by 3600, or 1.46667 ft/s. A useful reverse figure is that 1 ft/s equals about 0.6818 mph, so a vehicle at 60 mph covers 88 feet every second.
References
Background & Theory
1 m/s = 3.6 km/h exactly = 2.23693629 mph = 1.94384449 knots. The metre per second is the coherent SI unit; every other speed unit here is a length unit divided by a time unit, so the exactness of the length definition carries straight through.
Conversion reference table
| Conversion | Equivalent | Exact or rounded? |
|---|---|---|
| 1 metre per second | 3.6 kilometres per hour | Exact by definition |
| 1 mile per hour | 1.609344 km/h = 0.44704 m/s | Exact |
| 1 kilometre per hour | 0.621371192 mph = 0.277778 m/s | Derived, rounded |
| 1 knot | 1.852 km/h = 1.15077945 mph | Exact / derived |
| 1 metre per second | 1.94384449 knots | Derived, rounded |
| 1 foot per second | 0.3048 m/s = 0.681818 mph | Exact / derived |
| Speed of sound (15 C, sea level) | 340.29 m/s = 1,225.0 km/h | Standard atmosphere |
| Speed of light in vacuum | 299,792,458 m/s | Exact by definition |
Aviation and marine navigation use knots because the nautical mile is tied to one minute of latitude, which makes chartwork arithmetic trivial. Meteorology mixes conventions freely - wind speeds appear as knots, m/s, km/h and mph depending on the country and the audience - so a wind figure without its unit is worthless: 30 is a stiff breeze in knots and a gale in m/s.
Reviewed for accuracy by Manoj Kumar, Mathematics Educator · Editorial policy
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