Speed Converter
Kilometres per hour, miles per hour, metres per second, feet per second, knots and Mach — plus running pace, which is the same information upside down and is the one conversion most tables get wrong.
Convert a speed
The reading you have, in the unit chosen below.
The unit the reading is already in. The last two are paces, which count time per distance rather than distance per time.
The unit you want the answer in. Every other unit is listed underneath the result anyway.
Everything routes through the metre per second: 100 km/h is 27.77777778 m/s.
- Conversion factor
- 1 km/h = 0.6213711922 mph
- In metres per second
- 27.77777778 m/s
- Definition
- One international mile per hour. The mile has been exactly 1,609.344 m since 1959, so this is exactly 0.44704 m/s.
| Unit | Symbol | Value |
|---|---|---|
| Metres per second | m/s | 27.77777778 |
| Kilometres per hour | km/h | 100 |
| Miles per hour | mph | 62.13711922 |
| Feet per second | ft/s | 91.13444153 |
| Knots | kn | 53.99568035 |
| Mach (sea level, 15 °C) | Mach | 0.08162972105 |
| Minutes per kilometre | min/km | 0.6 (0:36) |
| Minutes per mile | min/mi | 0.9656064 (0:58) |
Six units multiply. Two of them divide.
Every unit here is stored as one number — how many metres per second it is worth — and every conversion goes through that base. For the six speed units that is the usual two-step multiply and divide:
m/s = value × f(from) • result = m/s ÷ f(to)- f(u)
- Metres per second in one unit u — 0.44704 for mph
- m/s
- The reading in the SI unit
- result
- The reading in the unit you asked for
Minutes per kilometre and minutes per mile break that pattern, because they are not speeds. They measure time per unit of distance, which is the reciprocal of distance per unit of time. So each unit carries a flag saying which kind it is, and the pace branch divides where the speed branch multiplies:
m/s = f(pace) ÷ value • pace = f(pace) ÷ m/s- f(min/km)
- 1000 m ÷ 60 s, or 16.6667
- f(min/mi)
- 1609.344 m ÷ 60 s, or 26.8224
That branch is its own inverse, which is what makes a round trip close: 5 min/km is exactly 12 km/h, and 12 km/h is exactly 5 min/km, with nothing lost in between. It also means that between a speed unit and a pace unit there is no conversion factor at all. What is constant instead is the product of the two readings. For km/h and min/km that product is 60, so any pair whose numbers multiply to 60 is the same motion: 100 and 0.6, 20 and 3, 12 and 5, 6 and 10.
The factors themselves are definitions rather than measurements. A mile has been exactly 1,609.344 m and a foot exactly 0.3048 m since the international yard and pound agreement of 1959; a nautical mile has been exactly 1,852 m since 1929. Only Mach is conditional, and it is labelled as such everywhere it appears.
Results are rounded to twelve significant figures rather than a fixed number of decimal places, because this form reaches Mach 0.08 and 91 ft/s from the same input, and no single decimal place reads well at both ends.
100 km/h, four ways
Step one: 100 × (1000 ÷ 3600) = 27.7778 m/s. Everything else comes off that one number.
- Miles per hour. 27.7778 ÷ 0.44704 = 62.14 mph. Note how far the rule of thumb misses: multiplying by 0.6 gives 60, which is 3.4% low, and on a motorway that is the difference between the limit and a ticket.
- Knots. 27.7778 ÷ 0.514444 = 54.00 kn. The near-round number is a coincidence of this particular speed, not a rule.
- Mach. 27.7778 ÷ 340.29 = Mach 0.0816 at sea level on a 15 °C day. In −57 °C air at cruising altitude the same speed would be about Mach 0.094, because sound itself has slowed down.
- Minutes per kilometre. Now divide instead: 16.6667 ÷ 27.7778 = 0.6 min/km, which is 0∶36 — thirty-six seconds a kilometre. Check it against the product rule: 100 × 0.6 = 60. ✓
And a running one, since that is where the reciprocal actually bites. A 5∶30 per kilometre pace is entered as 5.5, not 5.30. That converts to 8.851392 min/mi — which is 8∶51 per mile, not 8∶85, a number that does not exist. It is also 10.909 km/h, and 6.78 mph. If you want to work in the other direction — a finish time from a pace, or a pace from a finish time — that is the pace calculator.
What this converter assumes
- Mach is quoted at sea level, 15 °C — the ICAO standard atmosphere, where sound travels at 340.29 m/s. That is a condition, not a constant. Every other unit on this page has a fixed size; this one does not, and any Mach figure without a stated temperature is incomplete.
- Pace is entered in decimal minutes. 5 minutes 30 seconds is 5.5, not 5.30. The result panel prints the minutes and seconds form alongside the decimal so the two cannot be confused.
- A pace of zero is rejected. Zero minutes per kilometre is not a very fast runner, it is a division by zero. Zero is accepted as a speed, and the pace of something standing still is reported as unavailable rather than as a large number.
- The mile is the international mile of exactly 1,609.344 m, which fixes mph at exactly 0.44704 m/s. The US survey mile, about 2 parts per million longer, was retired for new work at the end of 2022 and is not offered.
- Speed here is scalar. There is no direction, no wind correction and no distinction between ground speed and air speed — all of which matter in aviation and none of which are unit conversion.
Speed conversion FAQ
What is 100 km/h in mph?
62.13711922 mph. A kilometre per hour is exactly 1000/3600 m/s and a mile per hour is exactly 1609.344/3600 m/s, so the ratio is exactly 1000/1609.344 — 0.6213711922 mph per km/h. The usual mental shortcut, multiply by 0.6, is about 2% low: it turns 100 km/h into 60 mph rather than 62.
Why does converting to minutes per kilometre work differently?
Because a pace is not a speed, it is a speed turned upside down. A speed counts distance per unit of time; a pace counts time per unit of distance. Going faster makes a speed bigger and a pace smaller, so the conversion is a division rather than a multiplication. There is no factor to multiply by — instead the product is fixed. In this pairing, km/h × min/km is always 60: 100 km/h is 0.6 min/km, 10 km/h is 6 min/km, 6 km/h is 10 min/km.
Is 5.5 minutes per kilometre the same as 5 minutes 50 seconds?
No — it is 5 minutes 30 seconds. Pace is written in minutes and seconds but calculated in decimals, and 0.5 of a minute is 30 seconds, not 50. This is the single most common pace mistake, and it is worth twenty seconds a kilometre, so this page prints both forms next to each other.
Why do ships and aircraft use knots instead of km/h?
Because a knot is one nautical mile per hour, and a nautical mile was defined as one minute of arc of latitude. That makes a speed in knots read directly as minutes of latitude per hour, so a navigator can step off distance on a chart using the latitude scale printed down its side — no conversion, no separate distance scale. The nautical mile has been exactly 1,852 m by international agreement since 1929, which no longer matches a minute of latitude perfectly, but the working convenience is why the unit stayed.
Is Mach 1 a fixed speed?
No, and that is why it is always quoted with conditions. Mach is a ratio to the local speed of sound, which depends on the temperature of the air — roughly the square root of absolute temperature. At sea level on a standard 15 °C day, sound travels at about 340.29 m/s, so Mach 1 is about 1,225 km/h. At a cruising altitude of 11 km, where the standard atmosphere is −56.5 °C, sound travels at about 295 m/s and Mach 1 is about 1,062 km/h. This page uses the sea-level figure, and labels it.
What speed is a 4-minute mile?
15 mph, or 24.14 km/h. Set the source unit to minutes per mile, enter 4, and read miles per hour: the constant for that pair is 60, so 60 ÷ 4 is 15. The same arithmetic explains why 60 mph is exactly one minute per mile — a mile a minute is where the phrase comes from.
Sources and review notes
- NIST Special Publication 811 — Guide for the Use of the International System of Units (SI), including the exact mile, foot and nautical mile factors used here
- BIPM — The International System of Units (SI) Brochure, for the metre and the second
- ICAO Doc 7488 — Manual of the ICAO Standard Atmosphere, the source of the 340.29 m/s sea-level speed of sound
The speed factors on this page are defined values rather than measured ones, so they do not go stale: the mile has been exactly 1,609.344 m since 1959 and the nautical mile exactly 1,852 m since 1929. The Mach figure is the only conditional number here, and it is fixed to a published standard atmosphere rather than to conditions anywhere in particular.