Supported units
- Meter per second (m/s)
- Kilometer per hour (km/h)
- Mile per hour (mph)
- Knot (kn)
Conversion tool
Speed Converter
Select a category, enter a value, and convert between compatible units.
Speed units explained
Speed describes the distance travelled during a given period of time. Metres per second is the SI unit, while kilometres per hour and miles per hour are common in transportation.
Common engineering uses
Speed conversion is used in vehicle specifications, transport, machinery, motion analysis and engineering calculations.
Formula
v = d / t
Average speed equals distance travelled divided by elapsed time. The SI unit is the metre per second. Instantaneous speed describes the rate of motion at a particular moment.
- v = speed, measured in metres per second (m/s)
- d = distance travelled, measured in metres (m)
- t = elapsed time, measured in seconds (s)
Common conversions
| From | Equivalent value |
|---|---|
| 1 metre per second (m/s) | 3.6 kilometres per hour (km/h) |
| 1 kilometre per hour (km/h) | approximately 0.277778 m/s |
| 1 mile per hour (mph) | 1.609344 kilometres per hour (km/h) |
| 1 knot (kn) | 1.852 kilometres per hour (km/h) |
| 1 foot per second (ft/s) | 0.3048 metre per second (m/s) |
| 1 metre per second (m/s) | approximately 2.23694 miles per hour (mph) |
Convert 90 km/h to m/s
- Use the relationship 1 km/h = 1/3.6 m/s.
- Divide 90 by 3.6.
- 90 / 3.6 = 25 m/s.
90 km/h = 25 m/s
This conversion changes only the unit. It does not distinguish between average and instantaneous speed.
Engineering applications
- Comparing vehicle, rail and transportation specifications.
- Calculating conveyor, actuator and machine-component motion.
- Evaluating airflow and fluid velocity in ducts and pipes.
- Using marine and aviation data expressed in knots.
- Converting test, laboratory and international performance data between unit systems.
Common mistakes
- Confusing speed with velocity. Velocity includes direction, while speed is a scalar magnitude.
- Converting distance units but forgetting to convert hours, minutes or seconds in the denominator.
- Treating revolutions per minute as a linear speed without including the rotating radius or diameter.
- Using a fixed conversion for Mach number even though the speed of sound depends on the medium and its temperature.
- Comparing average speed with a peak or instantaneous speed.
Frequently asked questions
How do I convert km/h to m/s?
Divide the value in kilometres per hour by 3.6.
How do I convert m/s to km/h?
Multiply the value in metres per second by 3.6.
How many km/h are in one mph?
One mile per hour equals exactly 1.609344 kilometres per hour.
What is a knot?
A knot is one nautical mile per hour, exactly 1.852 kilometres per hour.
Can Mach be converted using one fixed factor?
Not universally. Mach number is the ratio of an object's speed to the local speed of sound, which varies with conditions such as temperature.