Convert km/h to m/s kilometres per hour ↔ metres per second Free Online Secure
Type a value in kilometres per hour and read it in metres per second at once. The factor is exact by definition, the arithmetic happens in your browser, and nothing is sent anywhere.
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Convert from kilometres per hour
Convert to metres per second
Common values — Convert km/h to m/s (kilometres per hour ↔ metres per second)
| km/h | m/s |
|---|---|
| 1 | 0.277777777778 |
| 2 | 0.555555555556 |
| 3 | 0.833333333333 |
| 5 | 1.38888888889 |
| 10 | 2.77777777778 |
| 20 | 5.55555555556 |
| 50 | 13.8888888889 |
| 100 | 27.7777777778 |
Where these units come from
Speed has no unit of its own: it is a length divided by a time, so every trade simply kept the length it was already using. That is why the same motion is 100 km/h on a European road sign, 62 mph on an American one and 27.8 m/s in a physics problem. The knot is the oldest of them and the most literal: sailors paid out a line with knots tied at even spacing and counted how many ran through their fingers while a sand glass emptied, so the speed was read off in knots. One knot is one nautical mile per hour, and a nautical mile is a minute of latitude — which is why ships and aircraft still use it. The speed of light is the odd one out: since 1983 it is not measured but fixed at exactly 299,792,458 m/s, because the metre is now defined from it.
Where you meet them
Kilometres and miles per hour live on speedometers and road signs, metres per second in physics, engineering and wind reports, feet per second in ballistics and in American machine shops. Knots carry shipping, aviation and marine weather, and Mach numbers appear wherever an aircraft is fast enough for the air's own stiffness to matter. The speed of light turns up less in daily life than in distances: a light year is simply how far it gets in one.
Questions people ask
Is Mach 1 a fixed speed?
No. Mach is a ratio to the speed of sound in the surrounding air, and sound travels more slowly in colder air. This page uses the standard sea-level figure, 340.294 m/s, so Mach 1 here is about 1225 km/h. At the altitude airliners cruise at, the air is some 50 degrees colder and the same Mach 1 is roughly a tenth slower. An aircraft can therefore hold a constant Mach number while its speed over the ground changes.
Why do ships and aircraft use knots rather than km/h?
Because a nautical mile is one minute of arc of latitude. A vessel making one knot covers one minute of latitude in an hour, so speed, time and position on a chart fit together without conversion. The same reasoning kept the nautical mile at exactly 1852 metres rather than rounding it to something tidier.
Is the answer exact?
Where both units are defined in terms of one another by whole numbers, yes — the page says so above the figure, and the only rounding is in how many digits are shown. Where the ratio has no finite decimal, the page shows twelve significant digits and says the relation is approximate rather than pretending otherwise.
Does anything I type leave my device?
No. The arithmetic runs in your browser; nothing is uploaded and there is no server to upload it to. Load the page once and it keeps working with the network switched off.
Kinematics homework: from km/h to m/s before you calculate
Physics problems love to mix units. A car travels at 72 km/h, a train is 200 metres long, a stopwatch reads in seconds, and the question asks for an answer in metres. The formulas of motion need a consistent set of units, so a speed in kilometres per hour must be turned into metres per second first. To convert km/h to m/s, divide by 3.6: 36 km/h is 10 m/s, 72 km/h is 20 m/s and 108 km/h is 30 m/s. The calculator above divides as you type, and the sections below walk through typical problems and the checks that save marks.
You will find the rule with worked examples, a short profile of each unit, a comparison, a collection of solved problems and the slips to avoid. The arithmetic runs in your browser, and what you type is not sent anywhere.
How to convert km/h to m/s: divide by 3.6
The rule
One kilometre per hour is 1,000 metres in 3,600 seconds, which is 0.2778 m/s. To convert km/h to m/s, divide the km/h figure by 3.6. So 54 km/h is 15 m/s, 90 km/h is 25 m/s and 120 km/h is 33.33 m/s. To go the other way, multiply by 3.6.
Worked examples
A walking pace of 5 km/h is 1.39 m/s. A bicycle at 18 km/h is 5 m/s. A car at 100 km/h is 27.78 m/s, and a high-speed train at 300 km/h is 83.33 m/s.
Why 3.6
Convert each part: 1 km = 1,000 m and 1 h = 3,600 s. The ratio 1,000 over 3,600 is 1 over 3.6. Writing the units out in the working, a method called dimensional analysis, shows where the factor comes from and prevents slips.
A quick sanity test
The m/s figure is always 3.6 times smaller than the km/h figure. If a “convert km/h to m/s” calculation result is larger than the starting number, you multiplied instead of dividing.
The kilometre per hour
The everyday unit of speed
The kilometre per hour is the unit on car dashboards, road signs and train timetables. Problems set in the real world quote speeds this way because it matches what students see, but equations need a unit conversion before use.
Where it appears
Problem statements, speed limits, vehicle specifications and news.
The metre per second
The SI unit of speed
The metre per second belongs to the SI system. Newtons, joules and watts are defined with metres and seconds, so using m/s means a force of one newton gives one kilogram an acceleration of one metre per second squared.
Where it appears
Physics equations, laboratory data and engineering calculations.
Kilometres per hour against metres per second
One m/s equals 3.6 km/h. A figure in km/h is therefore 3.6 times bigger than the same speed in m/s. A car at 72 km/h travels 20 metres each second, which is easier to use in a formula for distance or braking. The factor is exact, so no rounding enters the conversion.
The usual trap is the direction. From km/h to m/s the number shrinks.
Where the conversion shows up
Problem 1: a train and a tunnel
A train 200 m long travels at 108 km/h through a tunnel 800 m long. How long does it take to pass completely through? Convert: 108 km/h is 30 m/s. The train must travel 800 + 200 = 1,000 m, which takes 1,000 divided by 30, or 33.3 seconds. A “convert km/h to m/s” calculation before the main calculation makes everything else straightforward.
Problem 2: overtaking
A car at 120 km/h follows a lorry at 90 km/h with a gap of 50 m. To overtake it must travel 50 m plus 20 m of length. The difference in speed is 30 km/h, which is 8.33 m/s. Time to pass is 70 divided by 8.33, or 8.4 seconds. During that time the car covers 8.4 × 33.3 = 280 m.
Problem 3: braking
A car at 72 km/h brakes with a deceleration of 5 m/s². The speed is 20 m/s, so it stops in 4 seconds and travels 20 × 20 / (2 × 5) = 40 metres. If the speed were 144 km/h, or 40 m/s, the stopping distance would be 160 m, four times as much.
Problem 4: kinetic energy
A 1,200 kg car travels at 54 km/h. What is its kinetic energy? Convert: 54 km/h is 15 m/s. The energy is half the mass times speed squared: 0.5 × 1,200 × 225 = 135,000 J, or 135 kJ. Using 54 directly would give 1,749,600 J, an answer 13 times too large. This is a classic error, which a “convert km/h to m/s” calculation prevents.
Problem 5: lightning and thunder
Sound travels at about 340 m/s, which is 1,224 km/h. If thunder arrives 3 seconds after lightning, the strike is 1,020 m away. This is a good example of mixing units: a problem might give the speed of sound in km/h and the delay in seconds. Converting to m/s makes the answer in metres follow at once.
Problem 6: relative speed head-on
Two cars approach each other at 50 km/h and 60 km/h on a straight road, 330 m apart. Their closing speed is 110 km/h, which is 30.6 m/s. They meet after 330 / 30.6 = 10.8 seconds. Adding speeds in km/h and then converting once is faster than converting each speed separately, but both methods give the same result.
Problem 7: escape and orbit
Escape velocity from Earth is 11.2 km/s, which is 40,320 km/h. The International Space Station moves at 7.66 km/s, or 27,576 km/h. These are the one place where physics problems give km/s, and the conversion to m/s is a factor of 1,000, not 3.6. A “convert km/h to m/s” calculation is not needed when the starting unit is km/s.
Problem 8: wheels and rotation
A car wheel of diameter 0.65 m rolling at 100 km/h, or 27.78 m/s, rotates at v divided by the circumference: 27.78 / 2.042 = 13.6 revolutions per second, or 816 per minute. Engineers use this to check speedometers. A tyre with a smaller radius spins faster for the same speed, which is why a mismatch gives a wrong reading.
Dimensional analysis in four lines
Write the speed with its unit, multiply by 1,000 m per km, divide by 3,600 s per hour, and cancel the units. For 90 km/h: 90 × 1,000 / 3,600 = 25 m/s. Every unit cancels except metres per second. This method works for any conversion, so students who adopt it never need to memorise 3.6.
Spreadsheet formulas
Place speeds in km/h in column A and use =A2/3.6 in column B. For the reverse, use =B2*3.6. Use column C for the distance in a given time, =B2*time_in_seconds. Label every column with its unit so that a reader can see at a glance what each number means.
Rounding in a physics answer
The factor 3.6 is exact, but 1/3.6 is an infinite decimal: 50 km/h is 13.8889 m/s. Keep at least four significant figures through the working and round only the final answer to the precision of the data. If the data are given to two figures, an answer of 14 m/s is enough.
A mental shortcut
Divide by 4 and add 10 per cent. For 100 km/h: 25 plus 2.5 gives 27.5 m/s, close to the exact 27.78. For 50 km/h: 12.5 plus 1.25 gives 13.75, against 13.89. For 36 km/h the shortcut gives 9.9, against an exact 10. It is fast enough to use in an exam.
Landmarks to memorise
18 km/h is 5 m/s, 36 km/h is 10 m/s, 54 km/h is 15 m/s, 72 km/h is 20 m/s, 90 km/h is 25 m/s, 108 km/h is 30 m/s and 144 km/h is 40 m/s. Each 18 km/h adds 5 m/s. These landmarks let you convert many exam speeds without arithmetic.
Reference ladder
5 km/h is 1.39 m/s. 10 km/h is 2.78 m/s. 30 km/h is 8.33 m/s. 50 km/h is 13.89 m/s. 70 km/h is 19.44 m/s. 100 km/h is 27.78 m/s. 130 km/h is 36.11 m/s. 200 km/h is 55.56 m/s. 300 km/h is 83.33 m/s. A ladder like this helps check your work.
Problem 9: acceleration from 0 to 100
A car accelerates from rest to 100 km/h in 8 seconds. Convert 100 km/h to 27.78 m/s. The average acceleration is 27.78 divided by 8, or 3.47 m/s², about 0.35 g. The distance covered is half the acceleration times time squared: 0.5 × 3.47 × 64 = 111 m. The numbers show why 0 to 100 times of 8 seconds are considered brisk, not extreme.
Checking by reversing
To check any convert km/h to m/s result, multiply it by 3.6. If 90 km/h became 25 m/s, then 25 times 3.6 is 90. A second test is the size: the m/s figure should be a little more than a quarter of the km/h figure.
Relation to mph and knots
1 m/s is 2.237 mph and 1.944 knots. A car at 25 m/s, which is 90 km/h, is at 55.9 mph and 48.6 knots. Problems written for American students use mph, and the same method applies: convert first to m/s, then use the formulas, then convert the answer to the unit asked for.
Exam strategy
Write the converted speed at the top of your working and mark it clearly. Examiners award marks for the correct conversion even if a later step fails. Underline the unit in the question, say whether the answer is wanted in m/s or km/h, and convert at the end if needed. Habit makes the “convert km/h to m/s” calculation step automatic.
Common sense checks
After a calculation, ask if the answer is plausible. A braking distance of 4 m at 100 km/h is too short, and 4 km is too long. Walking at 50 m/s would be a mistake of 3.6 in the other direction, since that is 180 km/h. Comparing with known speeds, such as 1.4 m/s for walking and 28 m/s for a motorway car, is a quick filter.
Problem 10: a cyclist on a hill
A cyclist rides at 18 km/h up a slope and then coasts down at 54 km/h. The speeds are 5 m/s and 15 m/s. Energy per kilogram changes from 12.5 J/kg to 112.5 J/kg, nine times as much for three times the speed. For a total mass of 95 kg that is 1,188 J against 10,688 J. A “convert km/h to m/s” calculation for each speed leads to the comparison.
Problem 11: a conveyor and an escalator
An airport walkway moves at 4 km/h, which is 1.11 m/s, and a passenger walks on it at 5 km/h, or 1.39 m/s, relative to the belt. The ground speed is 9 km/h, or 2.5 m/s. A 100 m walkway takes 40 seconds instead of 72. Adding speeds in one unit and converting once is quicker than converting each, and a “convert km/h to m/s” calculation at the end gives the time.
Problem 12: free fall
A stone dropped from a bridge 45 m high reaches the water at a speed of the square root of 2 × 9.81 × 45, which is 29.7 m/s. In km/h that is 107 km/h. Here the work is in m/s and the final answer is converted to km/h to give a feel. Students often forget that the last step goes the other way, multiplying by 3.6.
Problem 13: a curve
A car takes a bend of radius 100 m at 72 km/h. The speed is 20 m/s, so the centripetal acceleration is v squared over r: 400 / 100 = 4 m/s². That is 0.41 g, which dry tyres can supply but wet tyres might not. At 108 km/h, or 30 m/s, the acceleration would be 9 m/s², nearly 1 g, and the car would slide. Squaring the speed makes the conversion crucial.
Problem 14: projectile range
A ball is kicked at 108 km/h at 45 degrees. The speed is 30 m/s, so the range is v squared over g: 900 / 9.81 = 91.7 m in a vacuum. Air resistance would reduce it a lot. Starting with km/h in the working gives a nonsense number, so the conversion is the first line of the answer.
Problem 15: a horizontal launch
A stone is thrown horizontally at 108 km/h from a cliff 20 m high. The fall takes the square root of 2 × 20 / 9.81, or 2.02 s. The horizontal distance is 30 × 2.02 = 60.6 m. Convert first, then calculate time and distance in metres. A “convert km/h to m/s” calculation done mentally takes seconds when the speed is a round number like 108.
Problem 16: momentum
A 1,200 kg car at 54 km/h has a momentum of 1,200 × 15 = 18,000 kg·m/s. If it collides and sticks to a stationary 1,800 kg car, the combined speed is 18,000 / 3,000 = 6 m/s, which is 21.6 km/h. Here the problem starts and ends in km/h, with the working in m/s, which is typical of textbook questions.
Problem 17: power needed
A 1,200 kg car accelerating at 3 m/s² while travelling at 54 km/h, or 15 m/s, needs a power of force times speed: 1,200 × 3 × 15 = 54,000 W, or 54 kW, ignoring drag. At 108 km/h, or 30 m/s, the same acceleration needs 108 kW. The power depends on speed, so an error in the unit conversion carries straight into the answer.
Problem 18: a train braking
A train at 160 km/h, which is 44.4 m/s, brakes with a deceleration of 0.7 m/s². The stopping distance is v squared over 2a: 1,975 / 1.4 = 1,411 m, and the time is 63 seconds. Trains need more than a kilometre to stop, so signalling systems work in distances far longer than for road vehicles.
More values for convert km/h to m/s
A longer list of conversions
If the value you need is not in the first list, these further conversions may be close enough to read off directly:
- 0.1 km/h = 0.0277778 m/s
- 0.5 km/h = 0.138889 m/s
- 3 km/h = 0.833333 m/s
- 4 km/h = 1.11111 m/s
- 7 km/h = 1.94444 m/s
- 15 km/h = 4.16667 m/s
- 20 km/h = 5.55556 m/s
- 75 km/h = 20.8333 m/s
- 200 km/h = 55.5556 m/s
- 500 km/h = 138.889 m/s
- 2,000 km/h = 555.556 m/s
- 10,000 km/h = 2,777.78 m/s
Common slips when you convert km/h to m/s
Multiplying instead of dividing
From km/h to m/s the number gets smaller. If 90 km/h became 324, you multiplied.
Using 1,000/60
Dividing by 60 turns km/h into km per minute, not m/s. The hour has 3,600 seconds.
Forgetting to convert back
If the question asks for km/h, multiply the final m/s answer by 3.6 before writing it down.
Short answers
How do I convert km/h to m/s?
Divide by 3.6.
What is 90 km/h in m/s?
25 m/s.
What is 36 km/h in m/s?
10 m/s.
How many km/h is 1 m/s?
3.6 km/h.
Does my number leave my device?
No, the calculation runs in your browser.
More pages and a wrap-up
For other speed conversions see Convert km/h to Mach, Convert km/h to ft/s, Convert ft/s to m/s, Convert c to m/s, Convert m/s to knots, Convert km to mi, Convert mi to km, Convert °C to °F, Convert °F to °C. The reverse direction is Convert m/s to km/h.
In short, a “convert km/h to m/s” calculation means dividing by 3.6 and writing the unit beside the answer. Your number is computed locally, with no account and no upload.