Speed Converter

Convert speed between km/h, mph, m/s, knots, feet per second, Mach and the speed of light. Every factor is exact by definition except Mach, which is flagged as a reference condition.

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From

Value

mph

Result

1.60934 km/h

1 mph = 1.609344 km/h

Decimals

All units

Unit	Value
Kilometer per hour (km/h) (km/h)	1.60934
Meter per second (m/s) (m/s)	0.44704
Kilometer per second (km/s) (km/s)	4.4704E-4
Foot per second (ft/s) (ft/s)	1.46667
Mile per hour (mph) (mph)	1
Knot (nautical mile per hour) (kn)	0.868976
Mach (at 15 °C, sea level) (Mach)	0.00131369
Speed of light (c) (c)	1.49116E-9
Furlong per fortnight (fur/fn)	2,688

Training for a race? The running pace calculator works in minutes per kilometer instead of speed.

Ενημερώθηκε: 1 Αυγούστου 2026

Speed converter. Convert mph, km/h, knots, m/s and Mach.

A speed converter turns a speed in one unit into the same speed in another — mph into km/h, knots into mph — by scaling through the meter per second. Every factor here is fixed by international agreement except Mach, which follows the local speed of sound and therefore the air temperature.

What Is a Speed Converter?

A speed converter restates the same speed in a different unit by multiplying it through one fixed ratio: 1 mph is exactly 1.609344 km/h, 1 knot is exactly 1.852 km/h, and 1 m/s is exactly 3.6 km/h. None of those three figures came from a measurement. A speed is a distance divided by a time, and once both halves are pinned down by agreement — the international mile at 1,609.344 m since the 1959 International Yard and Pound Agreement, the nautical mile at 1,852 m since the Monaco hydrographic conference of 1929, the hour at 3,600 seconds — the ratio between any two speed units is fixed for good. That leaves precision as the only variable between one converter and another: how many digits it chooses to print.

The tool pivots everything through one base unit, the meter per second, which is the SI coherent unit for speed. Each supported unit carries a single factor to the meter per second, so any pair of units is two steps apart: scale the input up to m/s with the source factor, then scale back down with the target factor. Zero of any speed unit is zero m/s, so the whole conversion is one multiplication with no offset to add — the step that makes temperature conversion messier than this. Memorize a unit's value in m/s and you get every cross-conversion for that unit free.

Nine units sit in five groups, arranged around who uses them. The metric group covers the kilometer per hour, the meter per second and the kilometer per second, the last of which is how orbital and escape speeds are quoted: Earth's escape velocity is 11.186 km/s. The imperial group holds the foot per second and the mile per hour. The aviation and marine group holds the knot and Mach. A knot is one nautical mile per hour, and ships and aircraft use it because a nautical mile is close to one minute of arc of latitude, so 60 knots along a meridian works out to one degree of latitude per hour — chart work becomes arithmetic instead of conversion. The scientific group holds the speed of light in vacuum, exactly 299,792,458 m/s, a figure that carries no uncertainty because the meter has been defined from it since 1983. The novelty group holds the furlong per fortnight, which survives as a teaching device for dimensional analysis.

Mach is a ratio rather than a unit. Divide an object's speed by the local speed of sound and the answer is its Mach number, so Mach 0.85 means 85% of the speed of sound wherever the aircraft happens to be — and the speed of sound tracks air temperature. This converter pins Mach 1 to 340.294 m/s, the speed of sound in the ISO 2533 standard atmosphere at 15 °C and sea level, puts that condition inside the unit's own label, and marks every Mach result with ≈ instead of =. At the −56.5 °C of the tropopause, where airliners cruise, Mach 1 is closer to 295 m/s: about 660 mph rather than 761. That single asymmetry — eight factors fixed by definition, one reference condition that moves — is the rule worth carrying away from this page.

Common Speed Conversions and the Factors Behind Them

Conversion	Result	Underlying factor
1 mph → km/h	1.60934	× 1.609344 exactly
1 km/h → mph	0.621371	÷ 1.609344 exactly
1 knot → km/h	1.852	× 1.852 exactly
1 knot → mph	1.15078	1,852 ÷ 1,609.344 exactly
1 knot → m/s	0.514444	1,852 ÷ 3,600 exactly
1 m/s → km/h	3.6	× 3.6 exactly
1 m/s → mph	2.23694	1 ÷ 0.44704 exactly
1 ft/s → mph	0.681818	15 ÷ 22 exactly
60 mph → ft/s	88	88 exactly
100 km/h → mph	62.1371	100,000 ÷ 1,609.344 exactly
1 Mach → mph	761.216	not fixed — 15 °C, sea level
1 Mach → km/h	1225.06	not fixed — 15 °C, sea level
1 mph → furlong/fortnight	2688	2,688 exactly

The Speed Conversion Formula

v_{\text{target}} = v_{\text{source}} \times \dfrac{k_{\text{source}}}{k_{\text{target}}}

$v_{\text{source}}$ = The speed you start from, in the source unit
$k_{\text{source}}$ = Meters per second in one source unit — 0.44704 for mph, 0.3048 for ft/s, 1852/3600 for a knot
$k_{\text{target}}$ = Meters per second in one target unit
$v_{\text{target}}$ = The converted speed, in the target unit

Every speed conversion here is one multiplication and one division, because all speed units share the same zero: standing still reads 0 in every one of them. Give each unit a single number — how many meters per second it equals — and any pair of units is two scalings apart. Scale the input up to meters per second with the source factor, then scale back down with the target factor.

The factors are short enough to keep in your head. A kilometer per hour is 1000/3600 m/s. A mile per hour is 0.44704 m/s, since the international mile is 1,609.344 m and an hour is 3,600 s. A foot per second is 0.3048 m/s. A knot is 1852/3600 m/s. The speed of light is 299,792,458 m/s. A furlong per fortnight is 201.168/1,209,600 m/s. Each of those is a ratio of quantities that were themselves fixed by agreement rather than measured, so nothing built from them can drift.

NIST Special Publication 811, Appendix B.8 lists conversion factors and prints the exact ones in boldface. Foot per second appears there as 3.048 E−01 in bold, and mile per hour as 4.4704 E−01 in bold. Kilometer per hour (2.777 778 E−01) and knot (5.144 444 E−01) appear without bold, and the reason is typographic rather than physical: 1000/3600 and 1852/3600 are repeating decimals, and a printed decimal can never be exact. The ratios behind them are as fixed as the bold ones, so this converter treats both as exact and shows = on those pairs.

Mach needs a second equation, because the speed of sound in an ideal gas depends on temperature:

a = √(γ × R × T)

with γ = 1.4 for air, R = 287.05287 J·kg⁻¹·K⁻¹ (the specific gas constant for dry air fixed by ISO 2533) and T the absolute temperature in kelvin. Feed it the ISO 2533 sea-level standard day, T = 288.15 K, which is 15 °C, and it returns 340.294 m/s — the value this converter uses for Mach 1. Change T and the answer changes with it. Nothing in that equation is a definition, which is exactly why Mach pairs render with ≈ while the rest of the page renders with =.

Worked Speed Conversions

60 mph in km/h, ft/s and knots

A 60 mph limit is 96.5606 km/h. Multiply by the exact factor: 60 × 1.609344 = 96.56064 km/h, which the converter shows as 96.5606 at its default precision. The same 60 mph is 88 ft/s — a whole number with nothing rounded, since 60 miles is 316,800 feet and an hour is 3,600 seconds — and 52.1386 knots. Expand the all-units table under the result and all three appear at once, so a single entry answers the road, the classroom and the marine question together.

A 20-knot wind in mph, km/h and m/s

Twenty knots is 23.0156 mph, 37.04 km/h and 10.2889 m/s. The knot-to-km/h step is exact because the nautical mile is exactly 1,852 m: 20 × 1.852 = 37.04, with no rounding anywhere. Marine and aviation forecasts publish wind in knots while land forecasts publish it in mph or km/h, so this is the conversion that lets you line a sailing forecast up against a phone weather app. A 250-knot approach speed works the same way: 463 km/h exactly, or 287.695 mph.

Mach 1 at four air temperatures

Mach 1 moves with the air it is measured in. Because it is a ratio to the local speed of sound, the same Mach number is a different ground speed at every temperature:

At −56.5 °C, the tropopause temperature at and above 36,089 ft where airliners cruise: about 295.1 m/s, or 1,062 km/h and 660 mph.
At 0 °C: about 331.3 m/s, or 1,193 km/h and 741 mph.
At 15 °C, the ISO 2533 sea-level standard this converter uses: 340.3 m/s, or 1,225 km/h and 761 mph.
At 35 °C on a hot runway: about 351.9 m/s, or 1,267 km/h and 787 mph.

That is a spread of roughly 19% between the coldest and the warmest row. It is the reason the converter marks every Mach result with ≈ and prints the reference condition inside the unit's own label, where you see it before the number can mislead you.

Mach 2: 1,522 mph on the deck, 1,320 mph at cruise

Doubling the sea-level reference gives Mach 2 = 1,522.43 mph, or 2,450.12 km/h, at 15 °C. At the tropopause temperature the same Mach 2 is around 1,320 mph. Two hundred miles per hour separate those figures, and nothing but the air causes the difference. Read any published Mach speed for an aircraft alongside the altitude it applies to, or the number means little.

100 mph in feet per second — radar and physics homework

A 100 mph radar reading is 146.667 ft/s. The factor is exactly 22/15, the reciprocal of the 15/22 that runs the other way, because a mile is 5,280 feet and an hour is 3,600 seconds. The same relationship produces a pair of whole numbers worth memorizing: 60 mph is exactly 88 ft/s, and each extra 15 mph adds exactly 22 ft/s, so 45 mph is 66 ft/s and 75 mph is 110 ft/s. That makes ft/s the unit to reach for when you need a stopping distance or a reaction time, where seconds are already the denominator.

Escape velocity and a tenth of light speed

Earth's escape velocity of 11.186 km/s converts to 40,269.6 km/h and 25,022.4 mph. Kilometers per second is what keeps space figures readable — the same speed is 11,186 m/s, and in mph it needs five digits before the decimal. Push the scale further and 0.1 c comes out as 29,979.2 km/s, while light itself runs at 670,616,629 mph. At the far ends of the range the display switches to scientific notation: light speed in furlongs per fortnight lands near 1.8 × 10¹², and a furlong per fortnight in meters per second reads 1.663 × 10⁻⁴. A thirteen-digit integer and a row of leading zeros are both unreadable, so the tool spares you either.

1 mph in furlongs per fortnight

One mile per hour is exactly 2,688 furlongs per fortnight. The whole number is no accident: a mile is 8 furlongs and a fortnight is 336 hours, so 8 × 336 = 2,688 with nothing left over. One furlong per fortnight itself is 1.663 × 10⁻⁴ m/s, close enough to one centimeter per minute to be within about a quarter of a percent. Light covers 1.8026 × 10¹² furlongs per fortnight. The unit began as a joke and stayed on because classroom unit-conversion and dimensional-analysis exercises keep reaching for it.

How to Use the Speed Converter

The converter runs in three steps:

1. Pick the unit your figure is already in from the From menu. The nine units are filed under five headings — metric, imperial, aviation and marine, scientific, novelty — so the knot and Mach sit together rather than loose among the road units.

2. Pick the unit you want in the To menu. Both menus respond to the keyboard: with a list open, type the first letters of a unit's name to jump straight to it.

3. Type your value. The result updates as you type, and the copy button beside it puts the number with its symbol on the clipboard.

The page opens on mile per hour to kilometer per hour here and on kilometer per hour to mile per hour in the metric-locale versions, because the starting pair follows the measurement system of the language you are reading in. The swap button flips the two menus without touching your number, which saves re-picking when you realize you wanted the other direction. Under the result sits a Decimals selector: leave it on auto for about six significant figures, or fix 0, 2, 4, 6, 10 or 15 decimal places. Raise it when you want to see that 1 mph is 1.609344 km/h rather than the rounded 1.60934 the default shows.

Expand the all-units table below the result and the same speed appears in every supported unit at once, with your target unit highlighted. That view answers a wind forecast in knots, mph and m/s in one glance instead of three separate conversions, and it is where the Mach and speed-of-light rows earn their place. The Decimals setting governs that table too, so pushing it to 15 opens every digit of all nine conversions together.

To run the same math by hand, multiply by the source unit's value in meters per second and divide by the target's. Miles per hour to kilometers per hour needs only one number: multiply by 1.609344, so 65 mph is 104.607 km/h. Reverse it by multiplying kilometers per hour by 0.621371. The one pair that does not work this way is anything involving Mach, where the divisor is the local speed of sound rather than a defined factor — which is why those results carry ≈ and the rest carry =.

Common Speed Conversion Mistakes

Reading a knot as if it were a mile per hour. A knot is 1.15078 mph, so a 20-knot wind is 23.0156 mph, not 20. The gap is 15%, which is enough to put a crossing time or a flight-plan ETA badly out. Convert before you compare a marine or aviation figure against a road-speed one.
Saying "knots per hour". A knot already contains the hour — it is one nautical mile per hour. "Knots per hour" would describe an acceleration. Say "20 knots", and if you want the distance behind it, say "20 nautical miles in an hour".
Treating Mach 1 as a fixed 761 mph. Mach is a ratio to the local speed of sound, and that speed follows air temperature. The 761 mph figure holds at the 15 °C standard sea level this tool uses; at the −56.5 °C of the tropopause, Mach 1 is closer to 660 mph. Quote the altitude or the temperature alongside any Mach number.
Mixing up km/s with km/h. They differ by a factor of 3,600. Earth's escape velocity is 11.186 km/s, which is 40,269.6 km/h. Read the same figure as km/h and you are left with something slower than a bicycle.
Rounding 1 mph to 1.6 km/h. The defined factor is 1.609344. The shortcut is fine for eyeballing a speed-limit sign, but at 100 mph it lands 0.93 km/h short, and the error grows with every mile per hour you add.
Expecting minutes per kilometer out of a speed converter. Running pace is the reciprocal of speed: 12 km/h is 5:00 per kilometer, and doubling the speed halves the pace. No single multiplication turns one into the other, which is why pace lives in the running pace calculator instead of in this unit list.

Speed Units and Terms

Knot

One nautical mile per hour. The ISO symbol is kn; ICAO recommends kt in aviation. A knot is exactly 1.852 km/h, or 1.15078 mph, and it is the standard unit for airspeed, ship speed and wind.

Nautical mile

Exactly 1,852 meters, fixed by the First International Extraordinary Hydrographic Conference in Monaco in 1929. The United States adopted the international definition in 1954 and the United Kingdom in 1970. It is about 15% longer than the statute mile of 1,609.344 m used on roads.

Mach number

The ratio of an object's speed to the local speed of sound. It is dimensionless, so Mach 0.85 means 85% of the speed of sound in whatever air the aircraft is flying through, and it corresponds to a different ground speed at every temperature.

International Standard Atmosphere (ISA)

The reference atmosphere of ISO 2533, used throughout aviation. At sea level it fixes 15 °C (288.15 K), 101,325 Pa and a density of 1.225 kg/m³, with temperature falling 6.5 °C per kilometer up to the tropopause at 11,000 m (36,089 ft), where it settles at −56.5 °C.

Meter per second (m/s)

The SI coherent unit for speed, and the base this converter scales everything through. One meter per second is exactly 3.6 km/h and about 2.23694 mph.

Speed of light in vacuum (c)

Exactly 299,792,458 m/s. It carries no uncertainty because the meter has been defined from it since 1983: a meter is the distance light travels in 1/299,792,458 of a second.

Furlong per fortnight

A furlong (exactly 201.168 m) divided by a fortnight (1,209,600 s), giving 1.663 × 10⁻⁴ m/s — close to one centimeter per minute. It began as a joke unit and stayed on as a dimensional-analysis exercise.

Exact by definition

A conversion factor fixed by agreement rather than obtained from a measurement. The mile, the nautical mile, the meter and the second are all defined quantities, so the factors built from them — 1.609344, 1.852, 3.6 — will never be revised. Mach 1 is the one figure on this page outside that class.

Speed Converter — Frequently Asked Questions

How do I convert mph to km/h?

Multiply the miles per hour by 1.609344. So 60 mph = 96.5606 km/h and 100 mph = 160.934 km/h. The factor is exact, because the international mile is defined as exactly 1,609.344 meters.

How do I convert km/h to mph?

Multiply the kilometers per hour by 0.621371. So 100 km/h = 62.1371 mph and 50 km/h = 31.0686 mph. It is the reciprocal of 1.609344, so the two directions always agree with each other.

How fast is Mach 1 in mph?

Mach 1 is 761 mph at 15 °C and sea level, the standard-atmosphere reference this converter uses — 761.216 mph, or 1,225.06 km/h. That figure is not a fixed speed. Mach 1 tracks the local speed of sound, which falls as the air gets colder, so at the −56.5 °C of the tropopause where airliners cruise, Mach 1 is about 660 mph.

How fast is Mach 2 in mph?

At the 15 °C sea-level reference, Mach 2 is 1,522.43 mph, or 2,450.12 km/h. Up at cruise altitude, where the air sits near −56.5 °C, the same Mach 2 is around 1,320 mph. Quoting a Mach number without an altitude leaves a spread of roughly 200 mph, which is why aircraft specifications name the altitude alongside the Mach figure.

Is a knot the same as a mile per hour?

No. One knot is 1.15078 mph, because a knot is one nautical mile (1,852 m) per hour while a statute mile is 1,609.344 m. A knot is about 15% faster than a mile per hour, so 30 knots is 34.5234 mph.

Why do planes and ships use knots instead of mph?

Because a nautical mile is close to one minute of arc of latitude, a speed in knots reads straight off the latitude scale on a chart. A vessel holding 1 knot along a meridian covers about one minute of latitude in an hour, so 60 knots covers a full degree. Airspeed indicators, air traffic control instructions and marine forecasts all follow the same convention — ICAO recommends the symbol kt, while ISO uses kn.

How do I convert knots to mph and km/h?

Multiply knots by 1.15078 for mph and by 1.852 for km/h. A 20-knot wind is 23.0156 mph or 37.04 km/h; a 250-knot approach speed is 287.695 mph or 463 km/h. The 1.852 factor is exact, since the nautical mile is exactly 1,852 meters and an hour is 3,600 seconds.

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

Multiply by 3.6. An hour holds 3,600 seconds and a kilometer holds 1,000 meters, and 3,600 ÷ 1,000 = 3.6, so 10 m/s = 36 km/h. To reverse it, divide by 3.6.

How do I convert feet per second to mph?

Multiply by 15/22, which is 0.681818. The ratio comes from 3,600 seconds per hour divided by 5,280 feet per mile. So 100 ft/s = 68.1818 mph, and a 100 mph pitch or serve is 146.667 ft/s.

Why is 88 feet per second exactly 60 mph?

Because 60 miles per hour is 316,800 feet per hour, and dividing by 3,600 seconds gives exactly 88. The identity holds with no rounding at all, and the step between speeds is a whole number too: every extra 15 mph adds exactly 22 ft/s, since 5,280 feet per mile over 3,600 seconds per hour reduces to 22/15.

Is 1 mph exactly 1.609344 km/h?

Yes. The International Yard and Pound Agreement, signed on 1 July 1959 by six countries, fixed the yard at exactly 0.9144 meters, which puts the mile at exactly 1,609.344 meters. The kilometer and the hour are exact too, so the ratio never rounds. NIST prints the mile-per-hour factor in boldface in SP 811 Appendix B.8, which is its mark for a factor that is exact.

Why does the converter show ≈ instead of = on Mach results?

Because Mach 1 is a reference condition rather than a definition. Every other factor on this page is fixed by international agreement, so those pairs carry =. Mach is pinned to 340.294 m/s, the speed of sound at 15 °C and sea level in the ISO 2533 standard atmosphere, and that value moves with air temperature — so Mach pairs carry ≈. When you see the ≈, treat the number as valid for a standard sea-level day and check the real air temperature before you rely on it.

How fast is the speed of light in mph and km/h?

Light travels at exactly 299,792,458 m/s, which works out to 670,616,629 mph and 1,079,252,849 km/h. The value has no error bar on it: since 1983 a meter has been the distance light covers in 1/299,792,458 of a second, so the number is a definition. Enter a fraction such as 0.1 to see 29,979.2 km/s for a tenth of light speed.

Why does the converter include kilometers per second?

Because orbital and escape speeds are quoted that way. Earth's escape velocity is 11.186 km/s, which the converter turns into 40,269.6 km/h or 25,022.4 mph. Kilometers per second is also the readable unit for fractions of the speed of light, where meters per second runs to eight digits before the decimal point.

What is a furlong per fortnight?

A joke unit that behaves like a real one. A furlong is exactly 201.168 m and a fortnight is 1,209,600 seconds, so one furlong per fortnight is 1.663 × 10⁻⁴ m/s — close to a centimeter per minute. It lands on a memorable whole number: 1 mph is exactly 2,688 furlongs per fortnight, and light covers 1.8026 × 10¹² of them.

Can I get running pace in minutes per kilometer here?

No. Pace is the reciprocal of speed, so no single multiplication converts one into the other: 12 km/h is 5:00 per kilometer and 16 km/h is 3:45. The running pace calculator handles minutes per kilometer and minutes per mile directly.

How many decimal places can the converter show?

Up to fifteen. The Decimals selector under the result offers 0, 2, 4, 6, 10 and 15, plus an auto setting that holds about six significant figures. Set it to 6 and 1 mph reads as the full 1.609344 km/h rather than the 1.60934 auto shows; the higher settings pad that same value with trailing zeros.

How accurate is this speed converter?

Every factor except Mach is exact by international definition, so the only rounding is in the digits you choose to display — the conversion itself adds no error of its own. Mach is the single exception, since it assumes the 15 °C sea-level standard atmosphere rather than the air around you: expect it to run about 3% low on a hot sea-level day and about 15% high at airliner cruise altitude, where 761 mph should read 660.

Is this speed converter free?

Yes. It runs in your browser with no account and no usage limits, covering road, marine, aviation and scientific units. An embeddable version is available too, so aviation, sailing, motoring and physics sites can host the tool without sending readers off-site.

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