Speed Converter
Convert mph, km/h, knots, meters per second, Mach numbers, speed of sound and speed of light in one place. Enter a number in either field to see your result, current conversion factor and a speed conversion table.
Convert Speed Instantly
Type in either field, select your units, or use a popular conversion below.
At 15°C, the estimated speed of sound is 340.2923 m/s. Mach 1 and one “speed of sound” unit are equal at the selected air temperature. For ordinary mph, km/h or knots conversions, air temperature does not change the answer.
60 mph equals 96.56064 km/h
Popular speed conversions
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How to Use the Speed Converter
This calculator changes a speed value from one unit into another without changing the underlying speed. It supports common road, wind, science and aviation units, including Mach number under an air-temperature reference.
Enter a speed
Type a non-negative number into the From field, or enter a number in the To field to convert backward.
Choose both units
Select miles per hour, kilometers per hour, knots, Mach, meters per second or any other unit.
Check your answer
See the live result, formula and reference chart. When using Mach or sound units, set the dry-air temperature.
Speed Conversion Formula
The converter first expresses the entered speed in meters per second, then divides by the number of meters per second in the destination unit. This makes it possible to move between any of the 10 supported units.
General formula
Converted speed = Input × (m/s per source unit ÷ m/s per destination unit)
Example 1: 60 mph to km/h
One mile per hour equals exactly 1.609344 km/h. Therefore, 60 mph × 1.609344 = 96.56064 km/h.
Example 2: 20 knots to km/h
One knot equals exactly 1.852 km/h. Therefore, 20 knots × 1.852 = 37.04 km/h.
The worked example for your current unit selection: 5 mph × 1.609344 = 8.04672 km/h.
Speed Conversion Table
This conversion table updates with your two selected units. The displayed results are rounded for readability; calculations use the underlying conversion factors.
| Miles per hour (mph) | Kilometers per hour (km/h) |
|---|---|
| 1 | 1.609344 |
| 2 | 3.218688 |
| 5 | 8.04672 |
| 10 | 16.09344 |
The live table includes 1, 2, 5, 10, 25, 50, 100 and 1,000 source units. For Mach and speed of sound, it follows your selected air temperature.
Speed Units Explained
The following reference values express common speeds in meters per second. All fixed factors use established metric and international length definitions. Mach and speed of sound are condition-dependent.
| Unit | Equivalent in m/s | Typical context |
|---|---|---|
| Miles per hour (mph) | 0.44704 | Road speeds and weather reports |
| Kilometers per hour (km/h) | 0.277777777778 | Road and travel speeds |
| Knots (kn) | 0.514444444444 | Marine and aviation speeds |
| Meters per second (m/s) | 1 | Scientific measurement |
| Feet per second (ft/s) | 0.3048 | Engineering |
| Kilometers per second (km/s) | 1,000 | Astronomy and physics |
| Centimeters per second (cm/s) | 0.01 | Small-scale motion |
| Speed of light (c) | 299,792,458 | Light in vacuum |
| Mach 1 | About 340.2923 at 15°C | Relative to local speed of sound |
| One speed of sound (dry air) | About 340.2923 at 15°C | Reference speed of sound |
Mach Number vs. Speed of Sound
Why air temperature matters
Mach number is a ratio of a speed to the local speed of sound. In dry air, sound speed increases as absolute temperature rises. This tool estimates the speed of sound using the ideal-gas approximation a = √(γRT), with γ = 1.4, R = 287.05 J/(kg·K) and temperature T in kelvin.
At the default temperature of 15°C, Mach 1 and a unit labeled “speed of sound” are both approximately 340.29 meters per second. The estimate is a reference, not a substitute for a flight-specific atmospheric model.
Why speed of light is different
The speed of light option uses the exact vacuum value of 299,792,458 m/s. Unlike Mach 1, this reference does not change when the air temperature control changes.
For simple distance-over-time calculations, speed equals distance divided by elapsed time. To change the resulting unit, use the From and To dropdowns rather than recalculating the journey.
Measurement note: “Speed of sound” here means a dry-air reference at the chosen temperature, not sound speed in water or another gas. Real conditions, humidity and non-ideal gas effects can change the result. Negative speeds are excluded because this tool converts speed magnitudes, not signed directional velocity.
Frequently Asked Questions
How do I convert miles per hour to kilometers per hour?
Multiply mph by 1.609344. For example, 60 mph equals 96.56064 km/h. The converter supports both directions and displays the current formula.
How many kilometers per hour are in one knot?
One international knot equals exactly 1.852 kilometers per hour. It is based on one nautical mile (1,852 meters) per hour.
What is the difference between mph, km/h and m/s?
All three measure speed. Miles per hour and kilometers per hour describe distance traveled each hour; meters per second describes meters traveled each second. One m/s equals 3.6 km/h.
What does Mach 1 mean?
Mach 1 means moving at the local speed of sound in the selected medium. In this calculator it uses an ideal dry-air approximation, with temperature set to 15°C unless you change it.
Is the speed of sound always 343 m/s?
No. About 343 m/s is a common room-temperature reference, but it changes with air temperature and gas composition. Use the adjustable temperature field for an estimate in dry air.
Why are Mach number and speed of sound both listed?
Both are provided because people search for either reference. Here, Mach 1 and one speed-of-sound unit represent the same numerical speed in dry air at the chosen temperature.
Does the speed of light change with air temperature?
No. This tool defines one speed-of-light unit as the exact vacuum value of 299,792,458 m/s. Light travels more slowly in materials, but those medium-specific speeds are not used here.
Can I use negative values?
No. This calculator works with non-negative speed magnitudes. For directional velocities, direction needs to be represented separately from speed.
Why might my Mach result differ from another calculator?
Different tools may assume different air temperatures, gas constants or atmosphere models. Check the selected dry-air temperature and the assumptions before comparing results.
Does the calculator round conversion results?
Large or tiny numbers may display in scientific notation and normal results may show rounded digits. The conversion is calculated before the display rounding is applied.
Related Conversion Tools
Use these calculators when your question involves distance, elapsed time, or running pace instead of a direct speed-unit conversion.
Conversion References
The fixed speed factors follow defined international and metric units. The temperature-dependent Mach reference uses the ideal-gas sound-speed approximation described by NASA. Sources: NASA Glenn Research Center — Speed of Sound and NOAA — Wind speed conversion factors.