Speed converter
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- Formula shown below
- Reviewed
A speed converter changes a rate from one unit to another through metres per second as the base. One mile per hour is exactly 0.44704 metres per second, so 100 kilometres per hour equals 62.1371 miles per hour. One knot is exactly 1.852 kilometres per hour, because a nautical mile is defined as exactly 1,852 metres.
Result
100 km/h converted
62.13711922 mph
1 km/h = 0.6213711922 mph
- Conversion factor
- 1 km/h = 0.6213711922 mph
- Reverse factor
- 1 mph = 1.609344 km/h
- Rounded to 2 decimals
- 62.14 mph
100 km/h equals 62.13711922 mph. The conversion factor is 1 km/h = 0.6213711922 mph, and the reverse is 1 mph = 1.609344 km/h.
How to use the speed converter
- 01
Enter the speed
Type the value you want to convert. Decimals are accepted for precise readings.
- 02
Choose the source unit
Select the unit the reading is in: km/h, mph, m/s, knots or ft/s.
- 03
Choose the target unit
Select the unit you want the answer in. The result appears as you type, with no submit step.
- 04
Reuse the factor
The rows beneath the result show the conversion factor in both directions for use in a spreadsheet or calculation.
The formula
result = value × (factor_from ÷ factor_to)
- value
- The speed being converted.
- factor_from
- Metres per second per unit of the source unit — 0.44704 for mph.
- factor_to
- Metres per second per unit of the target unit.
- result
- The equivalent speed in the target unit.
Kilometres per hour convert to metres per second by dividing by exactly 3.6, since an hour holds 3,600 seconds and a kilometre holds 1,000 metres. That single factor is worth memorising, as it appears throughout physics problems.
Worked example
- Speed
- 100
- From
- Kilometres per hour
- To
- Miles per hour
- Result
- 62.13712 mph
Convert to the base unit first: 100 km/h ÷ 3.6 = 27.77778 m/s. Divide by the metres-per-second-per-mph factor: 27.77778 ÷ 0.44704 = 62.13712 mph. Both factors are exact by definition, so the conversion carries no approximation. The same speed is 53.9957 knots and 91.1344 feet per second.
Frequently asked questions
How do you convert km/h to mph?
Multiply the kilometres-per-hour figure by 0.621371. A speed of 100 km/h is 62.14 mph, 50 km/h is 31.07 mph, and 120 km/h is 74.56 mph. For a quick mental estimate, multiply by six and drop the last digit — 100 becomes 600, then 60, which is within four percent of the exact answer.
What is a knot and why is it used at sea and in aviation?
A knot is one nautical mile per hour, exactly 1.852 km/h or 1.15078 mph. Because a nautical mile equals one minute of latitude, a vessel travelling at 10 knots for one hour has moved exactly 10 minutes of latitude on the chart. That direct relationship to chart geometry is why marine and air navigation retain the unit.
How do you convert km/h to metres per second?
Divide by exactly 3.6. An hour holds 3,600 seconds and a kilometre holds 1,000 metres, so the ratio is 3,600 ÷ 1,000 = 3.6. A speed of 100 km/h is 27.78 m/s. To convert in the other direction, multiply metres per second by 3.6.
What is the speed of sound and how fast is Mach 1?
The speed of sound in dry air at 20 °C is 343 metres per second, which is 1,235 km/h or 767 mph. Mach 1 is the local speed of sound rather than a fixed value: it falls with temperature, so at typical cruising altitude, where air is around −55 °C, Mach 1 drops to roughly 295 m/s, or 1,062 km/h.
How fast is 60 mph in km/h?
Sixty miles per hour is 96.56 kilometres per hour. That is why the 0-to-60 mph acceleration figure used in the United States and the 0-to-100 km/h figure used elsewhere are not directly comparable — the metric benchmark is about 3.6% faster and consistently produces a slightly longer time.
What is the fastest speed possible?
The speed of light in a vacuum, exactly 299,792,458 metres per second, is the universal limit for information and matter. That value is a definition rather than a measurement: since 1983 the metre has been defined from it, which fixes the number exactly and leaves any refinement in measurement to adjust the metre instead.
Sources
- The International System of Units (SI Brochure) — Bureau International des Poids et Mesures
- NIST Guide to the SI — conversion factors — US National Institute of Standards and Technology
- Standard Atmosphere and the speed of sound — NASA Glenn Research Center
Last reviewed: · Formula and sources verified by Syed Aqeel Ahmad Gillani. See the methodology for how every calculation is derived.