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Speed Converter

Convert between metres per second, km/h, mph, knots, Mach number, feet per second, speed of light, and more — all speed and velocity units instantly.

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All conversions from 100 km/h

Unit	Symbol	Value

Sound (20°C): ~343 m/s, 1235 km/h, Mach 1 Light (vacuum): 299,792,458 m/s Earth escape velocity: 11,186 m/s

About This Tool

How this speed converter handles sixteen units, from feet per minute to the speed of light

Speed is distance over time, but the units people actually use range wildly in scale. A snail's pace and a jet airliner and a beam of light are all speeds, just separated by many orders of magnitude. This converter treats them all the same way, by anchoring every unit to metres per second and letting two multiplications handle the rest.

Everything runs client side in your browser using plain JavaScript. Nothing you enter leaves your device.

Why metres per second is the anchor

Metres per second is the SI derived unit for velocity, built directly from the base units of length and time. Because it is a coherent SI unit, every other unit in the table only needs a single multiplier to express itself in metres per second, rather than needing dozens of separate cross conversion formulas.

Step 1 Normalize to m/s The input multiplies by the source unit's factor. Entering 100 km/h becomes 100 times (1/3.6), which is roughly 27.78 metres per second.

Step 2 Convert to the target That m/s value divides by the target unit's factor. Converting to mph divides by 0.44704.

Step 3 Build the full table The same m/s figure is divided against all sixteen units simultaneously, giving a complete reference row rather than a single answer.

// adapted from the tool source, factor is m/s per 1 unit var SP = [ { key: 'kmh', factor: 1 / 3.6 }, { key: 'mph', factor: 0.44704 }, { key: 'knot', factor: 1852 / 3600 }, { key: 'c', factor: 299792458 } ]; var mps = val * fromUnit.factor; var result = mps / toUnit.factor;

Unit	Symbol	m/s per unit
Metres per second	m/s	1
Centimetres per second	cm/s	0.01
Kilometres per hour	km/h	0.277778 (1/3.6)
Kilometres per minute	km/min	16.6667
Kilometres per second	km/s	1,000
Miles per hour	mph	0.44704
Miles per minute	mi/min	26.8224
Miles per second	mi/s	1,609.344
Feet per second	ft/s	0.3048
Feet per minute	ft/min	0.00508
Knot	kn	0.514444
Mach (20°C, sea level)	Mach	343.0
Mach (11km altitude)	Mach(alt)	295.07
Speed of light (vacuum)	c	299,792,458
Metres per minute	m/min	0.016667 (1/60)
Inches per second	in/s	0.0254

Mach is not a fixed number of metres per second. Unlike every other unit here, Mach measures speed relative to the local speed of sound, which itself changes with air temperature and density. This tool offers two fixed reference points, one at 343 m/s for sea level air at 20 degrees Celsius, and one at 295.07 m/s representing conditions near 11 kilometres altitude where commercial jets cruise. Selecting either treats it as a constant multiplier, which is accurate at that specific altitude and temperature but will drift from a real Mach reading taken anywhere else in the atmosphere.

The one truly fixed entry in the table

Speed of light

Set at exactly 299,792,458 metres per second, a defined constant since the 1983 redefinition of the metre itself in terms of the speed of light and a fixed time interval. Unlike Mach, this value never varies with conditions.

The knot

Defined as one nautical mile per hour, at exactly 1852/3600 metres per second, about 0.514444. It remains the standard speed unit in marine and aviation navigation worldwide, tied to the nautical mile's basis in one minute of latitude.

SI derived unit, m/s Speed of light fixed by metre redefinition Mach varies with altitude

Speed unit references

BIPM SI Brochure defines the metre in terms of the fixed speed of light, 299,792,458 m/s, making that value exact by definition rather than measurement.
FAA aeronautical references document standard atmosphere assumptions used for Mach number and altitude relationships in aviation.
NIST SI derived units lists metres per second as the coherent SI unit for speed and velocity.

Speed in travel and in sport

Converting a car's speedometer reading between km/h and mph when driving abroad, checking wind speed reported in knots against a metric weather app, translating a treadmill's mph display into km/min pace for training logs, working out an aircraft's cruising speed in Mach against its actual ground speed, and sanity checking a physics problem that mixes imperial and metric velocity units.

Common Questions

Frequently asked questions

How do I convert km/h to mph?

Divide km/h by 1.609344, or multiply by about 0.621371. For example, 100 km/h is about 62.14 mph.

How do I convert m/s to km/h?

Multiply metres per second by 3.6. 10 m/s is 36 km/h. To go back, divide km/h by 3.6.

How fast is a knot?

One knot is one nautical mile per hour: exactly 1.852 km/h, about 1.15078 mph or 0.514444 m/s. It is the standard speed unit at sea and in aviation.

What speed is Mach 1?

Mach 1 is the local speed of sound, so it changes with air temperature. This converter uses 343 m/s (1,234.8 km/h) for air at 20 °C at sea level, and 295.07 m/s for the cold air near 11 km altitude.

Is this speed converter free?

Yes. It is free, needs no sign up, and every conversion runs in your browser, so nothing you type leaves your device.

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