This speed converter changes a speed between miles per hour, kilometers per hour, meters per second, knots, feet per second and other units. Every value goes through meters per second. The common factors are exact: 1 mph = 0.44704 m/s, 1 km/h = 1/3.6 m/s and 1 knot = 1,852 m per hour.
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How to use the speed converter
- Enter the speed, for example 100 from a road sign.
- Choose its unit and the unit you want, for example km/h to mph.
- Read the speed converter result: 100 km/h = 62.14 mph.
Quick factors: multiply mph by 1.609344 for km/h, and multiply m/s by 3.6 for km/h.
What is speed?
Speed is distance travelled per unit time. The SI unit is the meter per second. Road signs use km/h or mph (1 mph = 1.609344 km/h exactly), and ships and aircraft use knots (1 knot = 1.852 km/h).
Conversion formula
The speed converter stores every unit as a multiple of the base unit, the meter per second (m/s). To convert:
value in target unit = value × (factor of source unit ÷ factor of target unit)
where each factor is the size of the unit in meters per second.
Common speed conversions
| From | To | 1 unit equals |
|---|---|---|
| kilometer per hour (km/h) | mile per hour (mph) | 0.6213712 mph |
| mile per hour (mph) | kilometer per hour (km/h) | 1.609344 km/h |
| meter per second (m/s) | kilometer per hour (km/h) | 3.6 km/h |
| knot (kn) | mile per hour (mph) | 1.150779 mph |
| knot (kn) | kilometer per hour (km/h) | 1.852 km/h |
| foot per second (ft/s) | mile per hour (mph) | 0.6818182 mph |
| Mach (Ma) | kilometer per hour (km/h) | 1,225.044 km/h |
| meter per second (m/s) | foot per second (ft/s) | 3.28084 ft/s |
Speed converter worked example
Convert 25 kilometers per hour to miles per hour:
- Factor of km/h = 0.27777778 m/s
- Factor of mph = 0.44704 m/s
- 25 × 0.27777778 ÷ 0.44704 = 15.53428 mph
Speed unit reference
| Unit | Symbol | Group | Equals (m/s) |
|---|---|---|---|
| Meter per Second | m/s | SI | 1 |
| Kilometer per Hour | km/h | Metric | 0.2777777778 |
| Mile per Hour | mph | US/Imperial | 0.44704 |
| Knot | kn | Nautical | 0.5144444444 |
| Foot per Second | ft/s | US/Imperial | 0.3048 |
| Yard per Second | yd/s | US/Imperial | 0.9144 |
| Kilometer per Second | km/s | Metric | 1,000 |
| Mile per Second | mi/s | US/Imperial | 1,609.344 |
| Centimeter per Second | cm/s | Metric | 0.01 |
| Mach (approx., sea level, 20 °C) | Ma | Aerospace (approx) | 340.29 |
| Speed of Light in Vacuum | c | Physics | 299,792,458 |
Reverse factors for each speed unit
The speed converter reference table gives each unit in meter per seconds. To go the other way, divide by that factor; the list below does the division for you.
- Kilometer per Hour (km/h), Metric: 1 km/h = 0.2777778 m/s, so 1 m/s = 3.6 km/h.
- Mile per Hour (mph), US/Imperial: 1 mph = 0.44704 m/s, so 1 m/s = 2.236936 mph.
- Knot (kn), Nautical: 1 kn = 0.5144444 m/s, so 1 m/s = 1.943844 kn.
- Foot per Second (ft/s), US/Imperial: 1 ft/s = 0.3048 m/s, so 1 m/s = 3.28084 ft/s.
- Yard per Second (yd/s), US/Imperial: 1 yd/s = 0.9144 m/s, so 1 m/s = 1.093613 yd/s.
- Kilometer per Second (km/s), Metric: 1 km/s = 1,000 m/s, so 1 m/s = 0.001 km/s.
- Mile per Second (mi/s), US/Imperial: 1 mi/s = 1,609.344 m/s, so 1 m/s = 0.0006213712 mi/s.
- Centimeter per Second (cm/s), Metric: 1 cm/s = 0.01 m/s, so 1 m/s = 100 cm/s.
- Mach (approx., sea level, 20 °C) (Ma), Aerospace (approx): 1 Ma = 340.29 m/s, so 1 m/s = 0.00293867 Ma.
- Speed of Light in Vacuum (c), Physics: 1 c = 2.99792 × 108 m/s, so 1 m/s = 3.33564 × 10−9 c.
Speed limits: mph to km/h
Common US speed limits with their metric equivalents:
| mph | km/h | m/s |
|---|---|---|
| 25 | 40.2 | 11.18 |
| 30 | 48.3 | 13.41 |
| 35 | 56.3 | 15.65 |
| 45 | 72.4 | 20.12 |
| 55 | 88.5 | 24.59 |
| 65 | 104.6 | 29.06 |
| 70 | 112.7 | 31.29 |
| 75 | 120.7 | 33.53 |
| 80 | 128.7 | 35.76 |
For the reverse, divide km/h by 1.609344: a 50 km/h urban limit is about 31 mph.
Knots and nautical speed
Ships and aircraft use knots, one nautical mile per hour. The nautical mile is exactly 1,852 m, so 1 knot = 1.852 km/h ≈ 1.15078 mph ≈ 0.514 m/s. For knots to mph, multiply by 1.15078: a 250-knot airspeed is about 288 mph. Pace for runners is time per distance rather than speed; use the pace calculator for that.
Running pace and wind speed
Runners often think in pace, minutes per kilometer or per mile, rather than speed. Pace is 60 divided by speed. At 10 km/h the pace is 6:00 per kilometer; the speed converter gives 6.21 mph, which is a pace of about 9:39 per mile.
Weather reports use different units in different places. A 15 m/s wind is 54 km/h, about 33.6 mph and 29.2 knots. Aviation and marine forecasts use knots; road signs in the US and UK use mph; most other countries use km/h. Use the speed converter for the number and check which unit the source used before comparing forecasts.
Related converters and calculators
Related speed, distance and motion tools:
- mph to km/h: single-pair chart
- km/h to mph: single-pair chart
- Speed calculator: from distance and time
- Pace calculator: running pace
- Miles to km: distances
- Acceleration converter: m/s² and g
Sources
NIST Special Publication 811, Appendix B; NIST: SI units.
Questions about this calculator
What is the SI unit of speed?
Meters per second (m/s). Every unit in this converter is defined as a multiple of it.
How do I convert km/h to mph?
Divide by 1.609344. For example, 100 km/h = 62.14 mph.
How do I convert mph to km/h?
Multiply by 1.609344. For example, 65 mph = 104.6 km/h.
How do I convert knots to mph?
Multiply by 1.15078. For example, 30 knots = 34.5 mph.
How do I convert m/s to km/h?
Multiply by 3.6. For example, 10 m/s = 36 km/h.
How fast is the speed of sound?
About 343 m/s (1,235 km/h or 767 mph) in dry air at 20 °C. It changes with temperature, which is why Mach is not a fixed speed.
Check the assumptions and units before relying on a result. Financial, tax and health estimates do not replace advice for your individual circumstances.
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