Convert km/h to ft/s kilometres per hour ↔ feet per second Free Online Secure
Type a value in kilometres per hour and read it in feet 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 feet per second
Common values — Convert km/h to ft/s (kilometres per hour ↔ feet per second)
| km/h | ft/s |
|---|---|
| 1 | 0.911344415281 |
| 2 | 1.82268883056 |
| 3 | 2.73403324584 |
| 5 | 4.55672207641 |
| 10 | 9.11344415281 |
| 20 | 18.2268883056 |
| 50 | 45.5672207641 |
| 100 | 91.1344415281 |
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.
From the speedometer to the lab report: kilometres per hour in feet per second
A car's speedometer in most of the world reads in kilometres per hour. The engineering behind it, if it is described in an American paper, a standard or a simulation, is written with feet and seconds. Anybody who works on vehicle safety, drives an imported car across the United States, or just wants to follow a physics textbook with data in km/h needs a quick and reliable conversion. To convert km/h to ft/s, multiply by 0.9113: 50 km/h is 45.57 ft/s, 100 km/h is 91.13 ft/s and 130 km/h is 118.5 ft/s. The calculator above does the multiplication as you type, and the sections below show how the figures play out for helmets, bumpers, airbags and braking systems.
You will find the rule with worked examples, a profile of each unit, a comparison, a long run of practical cases and the mistakes people make most often. The calculation runs in your browser and your numbers are not sent anywhere. For regulatory work, always check the current text of the standard.
How to convert km/h to ft/s: multiply by 0.9113
The rule
One kilometre per hour is 1,000 metres in 3,600 seconds, which is 0.27778 m/s. One metre is 3.28084 feet, so 1 km/h is 0.27778 × 3.28084 = 0.91134 ft/s. To convert km/h to ft/s, multiply the number of km/h by 0.9113. That makes 30 km/h equal to 27.3 ft/s, 90 km/h equal to 82.0 ft/s and 250 km/h equal to 227.8 ft/s. To go the other way, multiply ft/s by 1.0973.
Worked examples
A car in a 30 km/h zone moves at 27.3 ft/s. On a country road at 90 km/h it covers 82 feet each second. A fast train at 320 km/h runs at 291.6 ft/s, and an airliner at 900 km/h travels at 820 ft/s.
Why the factor is exact
The factor comes from two definitions, the metre and the international foot of exactly 0.3048 metres. For fine work you can use 0.911344 and be sure of five good figures.
A quick sanity test
The answer in ft/s is almost 9 per cent smaller than the figure in km/h. If a “convert km/h to ft/s” calculation gave a larger number than you started with, you used the factor from the other direction.
The kilometre per hour
The unit on the dashboard
The kilometre per hour is the unit of road speed in nearly every country. Speed limits, speedometers, enforcement cameras and vehicle brochures are in it, and so are most test protocols for cars sold outside North America.
Where it appears
Road signs, speedometers, crash test protocols, brochures and timetables.
The foot per second
The unit of American mechanics
The foot per second is the speed unit of the US customary system and the one found in American physics textbooks, in older safety standards and in simulation code that uses g = 32.174 ft/s².
Where it appears
Textbooks, standards, simulation software and technical reports for American clients.
Kilometres per hour against feet per second
One km/h is 0.911 ft/s, so the figure in ft/s is nearly a tenth smaller. A speed of 100 km/h is 91.1 ft/s and one of 200 km/h is 182.3 ft/s. Both units describe the same motion, and only the scale differs.
The conversion is exact, with no hidden rounding. The usual trap is confusion with mph, which produces an error of almost 47 per cent.
Where the conversion shows up
Vehicle safety standards
Frontal crash tests are run at 56 km/h, 51.0 ft/s, in the older American protocol, and 64 km/h, 58.3 ft/s, in the offset tests used in Europe and by insurers in the United States. Pole tests are at 32 km/h, 29.2 ft/s. Reading a safety report from either side of the Atlantic often means a “convert km/h to ft/s” calculation for each test speed.
Low-speed bumper tests
Bumper regulations call for impacts at 4 km/h, which is 3.64 ft/s or 2.5 mph. Such a small speed matters because repair costs in car parks are high. The same test speed appears in the European and the American rules, written in different units.
Helmets and protective gear
A bicycle helmet is tested by dropping it from 1.5 metres, which gives an impact speed of 5.42 m/s, 19.5 km/h or 17.8 ft/s. A motorcycle helmet drop from 2.2 metres corresponds to 23.6 km/h, 21.6 ft/s. The numbers show how modest the test speed is compared with a car crash.
Airbag deployment
An airbag controller must decide in milliseconds whether a crash is severe enough to fire. A rough guide is the equivalent of hitting a rigid barrier at around 20 to 25 km/h, which is 18 to 23 ft/s. Lower speeds are handled by the seat belt alone. The actual threshold depends on the vehicle and on a computer's reading of the acceleration.
Precision in test reports
When you convert km/h to ft/s, bear in mind that if a speedometer is good to 1 km/h, giving the answer in ft/s to four decimals is misleading. Write 91.1 ft/s. Keep all the digits in the intermediate steps, and round only when you present the result, particularly where the speed enters an energy formula as a square.
Landmarks to memorise
10 km/h is 9.1 ft/s. 30 km/h is 27.3 ft/s. 50 km/h is 45.6 ft/s. 80 km/h is 72.9 ft/s. 100 km/h is 91.1 ft/s. 130 km/h is 118.5 ft/s. To convert km/h to ft/s by eye, interpolate between these anchors.
Reference ladder
5 km/h is 4.56 ft/s. 15 km/h is 13.67 ft/s. 25 km/h is 22.78 ft/s. 40 km/h is 36.45 ft/s. 60 km/h is 54.68 ft/s. 120 km/h is 109.36 ft/s. 160 km/h is 145.82 ft/s. 300 km/h is 273.40 ft/s. A table like this speeds up any check.
Checking by reversing
To check a “convert km/h to ft/s” calculation result, multiply the answer by 1.0973. If 100 km/h became 91.13 ft/s, then 91.13 times 1.0973 returns 100. A second test is the size: the number of ft/s should sit a little below the number of km/h.
Link to mph and m/s
One km/h is 0.6214 mph and 0.2778 m/s. To reach ft/s through mph, multiply by 1.4667. Through m/s, multiply by 3.2808. Both routes give 0.9113 for each km/h.
A worked example
A bus at 40 km/h brakes at 10 ft/s². Its starting speed is 36.45 ft/s and its braking distance is 36.45² / (2 × 10) = 66.4 feet, 20.2 metres. In SI units the deceleration is 3.048 m/s², the speed 11.11 m/s and the distance 11.11² / (2 × 3.048) = 20.2 metres. After a “convert km/h to ft/s” calculation, both routes agree.
Crumple zones
When a car hitting a barrier at 64 km/h, 58.3 ft/s, is stopped over 0.6 metres of crush, the mean deceleration is 26.9 g. The formula is v² / (2d) and works in any consistent unit set. Designers choose a long crush distance and a stiff passenger cell so the occupants see a lower peak.
Winds and storms
A category 1 hurricane starts at 119 km/h, which is 108 ft/s. A strong tornado can pass 300 km/h, 273 ft/s. Sound travels at 1,235 km/h, 1,125 ft/s. Weather agencies in the US report in mph and knots, while research papers favour m/s and ft/s.
Air resistance
At 100 km/h the air meets the car at 91.1 ft/s. Drag grows with the square of speed, so at 130 km/h, 118.5 ft/s, it is 69 per cent higher. This is why fuel use climbs steeply at motorway speeds.
Drones and light aircraft
A racing drone flies at 140 km/h, 127.6 ft/s, and a camera drone at 54 km/h, 49.2 ft/s. American drone rules use mph, whereas aerodynamics papers quote ft/s. A European manufacturer that exports needs to supply both.
Seat belt forces
A driver of 80 kg subjected to a deceleration of 30 g from 64 km/h, 58.3 ft/s, experiences a force near 23.5 kN on the whole body. Belts spread this over the chest and pelvis. A pretensioner removes slack in the first milliseconds so that the occupant is slowed together with the car.
Physics competitions
International physics contests use SI units, but some American competitions use ft/s. A student used to km/h has to convert km/h to ft/s quickly. A card in the pencil case with 36 km/h = 32.8 ft/s and 72 km/h = 65.6 ft/s saves time.
Driving in America
A visitor from abroad sees limits of 65 mph, which is 104.6 km/h or 95.3 ft/s. In one second at that speed the car covers 29 metres, 95 feet. Keeping that picture in mind helps to judge the distance to the vehicle ahead.
Sports photography
A photographer freezing a sprinter at 36 km/h, 32.8 ft/s, with a shutter of 1/1,000 of a second records a blur of 1 centimetre. At 1/250 the blur grows to 4 centimetres. American photography guides state the rules in feet per second, European ones in metres per second.
Walking and jogging
A walker moves at 5 km/h, 4.56 ft/s, and a light jogger at 10 km/h, 9.1 ft/s. A child of eight walks at about 4 km/h, 3.6 ft/s. These values are used to time pedestrian signals, for which American guidance assumes 3.5 ft/s.
Kinetic energy of a car
A car of 1,200 kg at 50 km/h, 13.9 m/s, has 116 kJ of kinetic energy. At 100 km/h it has 463 kJ. In American units these are about 85,400 and 341,500 ft-lbf. The unit of energy changes along with the unit of speed, but the physical reality is the same.
A second at a glance
At 36 km/h you cover 10 metres, 32.8 feet, in a second. At 72 km/h you cover 20 metres, 65.6 feet. Such landmarks give a feeling for speed and for the time available to react to an obstacle.
Radar tolerance
A road radar with a tolerance of 3 km/h below 100 km/h is accurate to 2.7 ft/s. A reported excess of 2 km/h cannot be proved if the tolerance is larger. American reports give the tolerance in mph or ft/s, and converting makes it possible to compare them with European practice.
Two routes to the same figure
You can convert km/h to ft/s directly with 0.9113, or in two steps: divide by 3.6 to get m/s and multiply by 3.2808. If the two routes disagree, a digit has been mistyped somewhere.
Imported measuring equipment
A speed gun or timing system imported from the US may display ft/s or mph. For metrological checks in other countries the result is presented in km/h. An instrument with a resolution of 0.1 ft/s resolves 0.11 km/h, and the certificate states the conversion factor used.
A table for teachers
A driving instructor explaining braking physics can use a table of speeds in km/h, m/s and ft/s: 50 km/h, 13.9 m/s, 45.6 ft/s; 90 km/h, 25 m/s, 82 ft/s; 130 km/h, 36.1 m/s, 118.5 ft/s. Students see quickly that one speed can be written three ways.
Equivalent drop height
A crash at 56 km/h has the same energy as a fall from 12.3 metres, 40.5 feet. At 64 km/h the figure is 16.1 metres, 52.9 feet. At 32 km/h it is only 4 metres, 13.2 feet. The relationship is quadratic, so doubling the speed means four times the height.
Driving simulators
Some simulators keep speed internally in feet per second and convert it to km/h for the display. A developer localising a title must check that 150 ft/s appears as 164.6 km/h and not as 150 km/h, because the 10 per cent error spoils the realism.
The foot and the metre
The foot came from the human body and the metre from the size of the Earth. Since 1959 the international foot has been defined through the metre as exactly 0.3048, so every conversion between them is stable worldwide, whichever country you work in.
Automatic emergency braking
Test protocols for automatic emergency braking use speeds from about 20 to 60 km/h, which is 18 to 55 ft/s. A car at 50 km/h, 45.6 ft/s, braking at 8 m/s² stops in 12.1 metres, after 1.74 seconds. The system has to detect the obstacle early enough for that distance to be available.
Pedestrian protection
Pedestrian tests fire impactors at the bonnet and windscreen at 40 km/h, 36.5 ft/s. This is the speed at which many urban collisions occur. Safety campaigns emphasise that a pedestrian struck at 30 km/h, 27.3 ft/s, has a far better chance of survival than one hit at 50 km/h, 45.6 ft/s.
Speed humps and calming
A raised crossing is designed to bring traffic down to about 15 km/h, 13.7 ft/s, and a school zone sets 30 km/h, 27.3 ft/s. In the United States such limits are posted as 10 and 20 mph. Whichever unit is used, drivers cover about 4 and 8 metres each second.
Stopping distance
On dry asphalt with a friction coefficient of 0.7, a car at 100 km/h, 91.1 ft/s, needs 56.2 metres, 184 feet, to stop once the brakes bite. With a reaction time of 1.5 seconds it travels another 41.7 metres, 137 feet. The total of nearly 98 metres is the figure behind the advice to keep a safe gap.
The mental shortcut
To convert km/h to ft/s in your head, subtract 9 per cent. For 100 km/h: 100 less 9 is 91, close to the exact 91.13. For 50 km/h: 50 less 4.5 is 45.5, against 45.57. The error is below 0.1 ft/s, good enough for a check on the road.
Spreadsheet formulas
To convert km/h to ft/s in a spreadsheet, put the km/h values in column A and enter =A2*0.911344 in column B. For the reverse, =B2/0.911344. Add a column that divides by 3.6 to give m/s, so you can compare the result reached through the two available routes.
More values for convert km/h to ft/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 = 0.0911344 ft/s
- 0.5 km/h = 0.455672 ft/s
- 3 km/h = 2.73403 ft/s
- 4 km/h = 3.64538 ft/s
- 7 km/h = 6.37941 ft/s
- 15 km/h = 13.6702 ft/s
- 20 km/h = 18.2269 ft/s
- 75 km/h = 68.3508 ft/s
- 200 km/h = 182.269 ft/s
- 500 km/h = 455.672 ft/s
- 2,000 km/h = 1,822.69 ft/s
- 10,000 km/h = 9,113.44 ft/s
Common slips when you convert km/h to ft/s
Multiplying by 1.0973
From km/h to ft/s the number falls. If 100 km/h turned into 110, you used the factor for the opposite direction.
Confusing it with mph
One km/h is not a mile per hour. 100 km/h is 62.1 mph or 91.1 ft/s. Mixing them produces an error of almost 47 per cent.
Rounding too early
If the speed is squared later in an energy or braking formula, keep the full digits until the end.
Quick questions
How do I convert km/h to ft/s?
Multiply the km/h figure by 0.9113.
How many ft/s is 100 km/h?
91.13 ft/s.
How many ft/s is 50 km/h?
45.57 ft/s.
How many km/h is 1 ft/s?
1.0973 km/h.
Is my input uploaded?
No, everything is calculated in your browser.
Where to go next
For other speed conversions see Convert km/h to knots, Convert km/h to Mach, Convert m/s to ft/s, Convert mph to ft/s, Convert ft/s to m/s, Convert km to mi, Convert mi to km, Convert °C to °F, Convert °F to °C. The reverse direction is Convert ft/s to km/h.
To sum up: kilometres per hour become feet per second when you multiply by 0.9113, and the unit goes next to the answer. What you type is processed on your own device, with no sign-up and no upload.