About Speed Converter
Convert between common speed-converter units instantly. Free online converter. Free, no sign-up required.
How to use
- Type your speed into the Value field. Decimals are fine — 65.5 mph or 0.05 m/s both work and the result updates the moment you stop typing.
- Pick the source unit from the From dropdown. Available: meters per second (m/s), kilometers per hour (km/h), miles per hour (mph), knots (nautical miles per hour), and feet per second (ft/s).
- Choose the target unit in the To dropdown. The default pairing is km/h to mph for road-trip math; switch to knots for sailing or aviation, or to m/s for physics calculations.
- Use the swap button between the dropdowns to instantly reverse the conversion direction. Useful for verifying a result by running it back through the inverse factor.
- Read the converted speed in the highlighted result box, formatted with up to 4 decimal places. For everyday use this is way more precision than you need; for engineering the underlying math carries full double-precision throughout.
- Need Mach or the speed of light? Mach 1 ≈ 343 m/s in dry air at 20 °C (it varies with temperature and altitude). The speed of light c = 299,792,458 m/s exactly — divide your m/s value by that to get fraction-of-c.
Examples
Highway speed in three units
100 km/h = 62.137 mph = 27.778 m/s = 53.996 knots. Most Canadian and European highways are signed in km/h; Americans see the same speed as 'about 62 mph.' At 100 km/h you cover 27.78 m every second — useful for stopping-distance estimates.
Cruise at altitude
A Boeing 737 cruising at 480 knots true airspeed equals 552.4 mph or 889 km/h. Aviation uses knots because nautical miles map directly to lines of latitude on charts — speed and chart distance share the same unit, so dead-reckoning navigation needs no conversion.
Walking and running
A casual walk at 5 km/h equals 1.39 m/s or 3.107 mph. Marathon pace at 12 km/h is 7.456 mph or 3.33 m/s. Usain Bolt's 100 m record translates to a peak of about 12.4 m/s (44.7 km/h, 27.8 mph) — faster than the average city speed limit.
Frequently asked questions
How do I convert miles per hour to kilometers per hour?
Multiply mph by 1.609344 to get km/h. So 60 mph × 1.609344 ≈ 96.56 km/h. For mental math, multiply by 1.6 — accurate within 0.6%, fine for everyday estimates. The exact factor comes from 1 mile = 1,609.344 m exactly (international yard and pound agreement, 1959), which makes the speed conversion a direct application of the length conversion.
How fast is a knot compared to mph?
1 knot = 1.150779 mph = 1.852 km/h = 0.5144 m/s. A knot is 1 nautical mile per hour, and the nautical mile (1,852 m) is defined as one minute of latitude. Aviation and maritime navigation use knots because the unit aligns with chart geometry — distance flown in nautical miles equals angular displacement on the chart, no conversion required. 30 knots ≈ 34.5 mph or 55.6 km/h.
What is the speed of sound in different units?
In dry air at 20 °C: 343 m/s = 1,235 km/h = 767 mph = 667 knots = 1,125 ft/s. This is Mach 1 by definition. Sound speed depends on the medium and temperature: at 0 °C it drops to 331 m/s, at 30 °C it rises to 349 m/s. In water it is roughly 1,480 m/s; in steel, 5,960 m/s. Aircraft Mach numbers reference the local atmospheric sound speed, which varies with altitude.
What is Mach number and how does it relate to speed?
Mach number is the ratio of an object's speed to the local speed of sound. Mach 1 means you are travelling at exactly the local sound speed. Because sound speed varies with temperature (and indirectly altitude), Mach 1 in m/s is not constant: 343 m/s at sea level / 20 °C, but only about 295 m/s at typical airliner cruising altitude. This converter uses sea-level standard for the Mach reference; precision aerospace work needs altitude-corrected calculations.
How do I convert m/s to km/h quickly in my head?
Multiply m/s by 3.6 to get km/h, or divide km/h by 3.6 to get m/s. The factor comes from there being 3,600 seconds per hour and 1,000 m per km, so the unit conversion is exactly 3,600 / 1,000 = 3.6. Physics problems and SI engineering use m/s; everyday traffic uses km/h almost everywhere outside the US. The 3.6× rule of thumb is one of the most useful in unit conversion.
What is the speed of light?
Exactly 299,792,458 m/s in vacuum — this is c, the universal speed limit. That equals 1,079,252,848.8 km/h, or 670,616,629 mph, or 983,571,056 ft/s. Since 1983, the meter has been defined by c (the distance light travels in 1/299,792,458 second), making c exact by definition rather than measured. This converter does not include c as a unit, but you can divide any m/s value by 299,792,458 to express it as a fraction of c.
Why do US speed limits use mph but science uses m/s?
The US, UK, and a handful of other countries kept imperial units for road signage despite metric being the international standard for science, engineering, and trade. Scientific work uses SI base units (meters, seconds), making m/s the natural speed unit. Engineers split the difference: civil engineering in the US still uses ft/s for hydraulics and traffic flow; aerospace uses both Mach and knots; physics uses m/s. This converter handles all of them.
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