Convert mph to ft/s miles per hour ↔ feet per second Free Online Secure
Type a value in miles 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.
Nothing uploaded
Convert from miles per hour
Convert to feet per second
Common values — Convert mph to ft/s (miles per hour ↔ feet per second)
| mph | ft/s |
|---|---|
| 1 | 1.46666666667 |
| 2 | 2.93333333333 |
| 3 | 4.4 |
| 5 | 7.33333333333 |
| 10 | 14.6666666667 |
| 20 | 29.3333333333 |
| 50 | 73.3333333333 |
| 100 | 146.666666667 |
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.
Miles per hour to feet per second: the arithmetic behind braking, cornering and acceleration
In the United States a speedometer reads miles per hour, yet the equations for braking, cornering and acceleration are written in feet and seconds. A stopping distance of 120 feet, an acceleration of 32 ft/s² and a speed of 88 ft/s go naturally together. To convert mph to ft/s, multiply by 1.4667, which is exactly 22/15: 60 mph is 88 ft/s, 100 mph is 146.7 ft/s and 150 mph is 220 ft/s. The calculator above multiplies as you type, and the sections below show how the figures are used for stopping distances, lane merges and launch times.
The page covers the rule with worked examples, a profile of each unit, a comparison and many everyday driving cases, followed by the common mistakes. The calculation runs in your browser and nothing you enter is sent anywhere. For real-world driving, follow the law and the conditions on the road.
How to convert mph to ft/s: multiply by 1.4667
The rule
There are 5,280 feet in a mile and 3,600 seconds in an hour, so a speed of one mph equals 5,280 / 3,600 = 1.466667 ft/s, which is exactly 22/15. Take your mph number and multiply it by 1.4667 to convert mph to ft/s: 15 mph comes to 22 ft/s, 45 mph to 66 ft/s and 200 mph to 293.3 ft/s. Reverse the process with 0.6818.
Worked examples
A car at 30 mph moves at 44 ft/s. A school-zone limit of 20 mph is 29.3 ft/s. A highway speed of 70 mph is 102.7 ft/s, and a top speed of 200 mph is 293.3 ft/s.
Why the factor is exact
The statute mile is exactly 5,280 feet and the hour exactly 3,600 seconds. The ratio 22/15 has no rounding in it; a decimal appears only when you write it as 1.4667.
A quick sanity test
The figure in ft/s is about half as large again as the figure in mph. If a “convert mph to ft/s” calculation gave a smaller number than you started with, you used the factor in the wrong direction.
The mile per hour
The unit on the dashboard
The mile per hour is the speed unit of everyday driving in the United States and the United Kingdom. Speed limits, speedometers, car reviews and weather reports all quote it.
Where it appears
Road signs, speedometers, reviews, broadcasts and weather bulletins.
The foot per second
The unit of calculation
The foot per second is what you get when distance is in feet and time in seconds. It is the natural unit for working out stopping distances and accelerations, because gravity is 32.174 ft/s² and distances on the road are posted in feet.
Where it appears
Physics problems, accident reconstruction, braking tests and traffic-engineering manuals.
Miles per hour against feet per second
One mph is 1.467 ft/s, so the figure in ft/s is about half as large again. A speed of 30 mph is 44 ft/s and one of 100 mph is 146.7 ft/s. Both describe the same motion, and only the size of the unit differs.
The conversion is exact, with no hidden rounding. The only trap is direction: from mph to ft/s the number grows.
Where the conversion shows up
Stopping distance
At 60 mph, 88 ft/s, a driver with a reaction time of 1.5 seconds travels 132 feet before touching the brake. On dry asphalt with a friction coefficient of 0.7 the braking distance is 88² / (2 × 0.7 × 32.174) = 172 feet, so the total is about 304 feet. A “convert mph to ft/s” calculation is the first step in every such calculation.
Acceleration tests
A car that goes from 0 to 60 mph in 4 seconds has reached 88 ft/s, so its mean acceleration is 22 ft/s², which is 0.68 g. In 3 seconds the figure is 29.3 ft/s², 0.91 g. Reviews give the time, physicists want the acceleration, and the bridge between them is the speed in ft/s.
Cornering
Lateral acceleration is v² divided by the radius. A car at 60 mph, 88 ft/s, on a bend of 500 feet radius feels 15.5 ft/s², which is 0.48 g. The same bend taken at 45 mph, 66 ft/s, gives 8.7 ft/s², 0.27 g. Highway engineers use these figures to post advisory speeds on curves.
The stopping-distance table
With a 1.5 second reaction time and 0.7 g of braking, the total stopping distance is about 63 feet at 20 mph, 109 feet at 30 mph, 164 feet at 40 mph, 229 feet at 50 mph, 304 feet at 60 mph and 388 feet at 70 mph. In ft/s the starting speeds are 29.3, 44, 58.7, 73.3, 88 and 102.7. The growth is faster than the speed, because braking distance follows its square.
Rounding and display
For a leaflet, 60 mph is simply 88 ft/s. For a calculation, 65 mph is 95.33 ft/s, and you should keep that. Round the final result only, and to no more digits than the original measurement justifies.
Landmarks to memorise
15 mph is 22 ft/s. 30 mph is 44 ft/s. 45 mph is 66 ft/s. 60 mph is 88 ft/s. 75 mph is 110 ft/s. 90 mph is 132 ft/s. 120 mph is 176 ft/s. To convert mph to ft/s by eye, start from 60 mph = 88 ft/s and scale up or down.
Reference ladder
1 mph is 1.47 ft/s. 5 mph is 7.33 ft/s. 10 mph is 14.67 ft/s. 25 mph is 36.67 ft/s. 55 mph is 80.67 ft/s. 70 mph is 102.67 ft/s. 130 mph is 190.67 ft/s. 200 mph is 293.33 ft/s. A table like this makes checking easy.
Checking by reversing
To check a “convert mph to ft/s” calculation result, multiply the answer by 0.6818. If 60 mph became 88 ft/s, then 88 times 0.6818 returns 60. A second test is size: the number in ft/s should be about one and a half times the number in mph.
Link to km/h and knots
One mph is 1.609 km/h and 0.869 knots. A car at 100 mph is going 160.9 km/h and 146.7 ft/s. European drivers read km/h, aviators and sailors read knots, and engineers who write the formulas use ft/s.
A worked example
A car at 70 mph stops in 170 feet. Its speed is 102.7 ft/s, so the deceleration is 102.7² / (2 × 170) = 31 ft/s², about 0.96 g. That is a very hard stop, near the limit of grip. The result could not be reached from the mph figure directly without a “convert mph to ft/s” calculation.
The drag strip
A quarter mile is 1,320 feet. A car that covers it in 13 seconds averages 101.5 ft/s, or 69 mph. If acceleration is constant, the trap speed at the line is twice the average, about 138 mph, or 202 ft/s. A drag racer's time slip prints elapsed time and trap speed in mph.
Sports in feet per second
A baseball pitched at 100 mph is moving at 146.7 ft/s and reaches the plate in 0.41 seconds. A golf ball hit at 170 mph is at 249 ft/s, and a tennis serve at 130 mph is at 190.7 ft/s. Broadcasts quote mph, while motion analysis uses ft/s.
Motor racing
An Indy car at 240 mph is moving at 352 ft/s on a straight, and a stock car at 200 mph is at 293 ft/s. Teams model aerodynamics and braking with ft/s and ft/s², but spectators want the figures in mph.
Wind and weather
A 25 mph wind is 36.7 ft/s, a storm at 60 mph is 88 ft/s and a hurricane at 120 mph is 176 ft/s. Wind pressure rises with the square of the speed, so these figures matter when engineers size roofs and signs.
Hard braking in tests
Consumer tests brake from 60 mph, 88 ft/s, to rest. A distance of 110 feet means a deceleration of 35.2 ft/s², which is 1.09 g, a sports-car result. A distance of 140 feet is 0.86 g, normal for an ordinary family car. The tests report feet, so the calculation needs the speed in ft/s.
Boats and rivers
A motorboat at 30 mph moves at 44 ft/s. A fast river of 5 mph flows at 7.3 ft/s. Manuals for recreational boaters quote mph, but resistance calculations are done in ft/s.
Light aircraft
A light aeroplane lifts off at 60 mph, 88 ft/s. With a mean acceleration of 0.2 g, 6.43 ft/s², the ground roll is 88² / (2 × 6.43) = 602 feet. A headwind of 15 mph, 22 ft/s, shortens the roll noticeably. Handbooks list distances in feet, so pilots and engineers work in ft/s.
Lifts and escalators
A fast lift in a tall building reaches 20 mph, 29.3 ft/s, and the fastest in the world nearly 46 mph. An escalator moves at 1 mph, 1.47 ft/s. Lift specifications in the US are in feet per minute, so ft/s serves as a check between mph and ft/min.
Free fall
A skydiver reaches 120 mph, 176 ft/s. After a fall of three seconds the speed is 96.5 ft/s, 65.8 mph, but a human reaches terminal speed only after about 12 seconds, since air resistance builds up gradually.
Sound and supersonic flight
Sound travels at 767 mph, 1,125 ft/s. A supersonic aircraft at 1,354 mph, 1,986 ft/s, is flying at Mach 1.8 at sea level. For a pilot the Mach number matters more than mph or ft/s.
Speed and energy
The energy of a body at 60 mph, 88 ft/s, is half its mass times 88 squared. At 120 mph, 176 ft/s, the energy is four times as great. The difference between 60 and 70 mph, 88 and 102.7 ft/s, is 36 per cent more energy.
Reading a data sheet
An American data sheet may show "65 mph (95 ft/s)". The figure in brackets is for calculation and the one before it for communication. When you see only a number, check the unit before using it, because mph and ft/s differ by almost 47 per cent.
A table for students
A small table in the notebook can prevent many errors in a “convert mph to ft/s” calculation: 15 mph = 22 ft/s, 30 mph = 44 ft/s, 45 mph = 66 ft/s, 60 mph = 88 ft/s. Students quickly learn that 60 mph = 88 ft/s is a base from which they can scale to any other value.
Radar tolerance
A road radar with a tolerance of one mph can be wrong by 1.47 ft/s. A report stating that a driver was doing 67 mph, 98.3 ft/s, in a 65 mph, 95.3 ft/s, zone shows an excess of 3 ft/s, which is small but measurable.
Game engines
Racing games may show mph on screen while the physics engine works in ft/s. A car at 150 mph is 220 ft/s in the code. Developers adapting a game for other markets must know which unit the constants use.
Electric cars and launch
An electric car that reaches 60 mph in 1.99 seconds accelerates at 44.2 ft/s², which is 1.37 g. A family hatchback needing 8 seconds averages 0.34 g. Because the number of feet travelled in launch is half the acceleration times the time squared, the quick car covers only 88 feet in the first two seconds.
Delivery drones
American rules restrict small drones to 100 mph, 146.7 ft/s, over the ground. A drone cruising at 33 mph moves at 48.4 ft/s. A manufacturer that quotes performance in mph should also give ft/s for the customer's energy calculations.
History of the mile and the foot
The mile began as a thousand Roman paces, and the foot as the length of a human foot. The modern definitions, 5,280 feet to the mile and 0.3048 metres to the foot, were fixed after 1959, so every conversion between them is exact.
Hydroplaning
A common rule estimates the speed at which a tyre starts to hydroplane as 9 times the square root of the tyre pressure in psi. For 35 psi that is 53 mph, 78 ft/s. Above that speed on a flooded road a tyre rides on a film of water. Drivers rarely think in ft/s, but the numbers show how little time there is to react.
Merging onto a motorway
A car that accelerates from 0 to 65 mph in 10 seconds averages 9.5 ft/s², which is 0.3 g. Its final speed is 95.3 ft/s, and it covers 476 feet in those 10 seconds. A slip road shorter than that forces a driver to merge slower than the traffic, which is dangerous.
Crash energy
A car at 35 mph, 51.3 ft/s, that stops over 2 feet of crush experiences a mean deceleration of 659 ft/s², about 20 g. At 70 mph, 102.7 ft/s, the same crush gives 82 g. That is why crumple zones need as much length as the designers can fit into the car.
Airbag and bumper thresholds
An airbag is not meant to fire in a minor impact. A rough threshold is an equivalent barrier crash at 14 mph, 20.5 ft/s. Bumpers must withstand impacts at 2.5 mph, which is 3.67 ft/s, without damage to safety systems. A “convert mph to ft/s” calculation shows how small such speeds are.
The mental shortcut
To convert mph to ft/s in your head, multiply by 3, halve it and subtract 2 per cent. For 60 mph: 90 less 1.8 is 88.2, close to the exact 88. For 100 mph: 150 less 3 is 147, against 146.7. The error is under 0.3 per cent.
Spreadsheet formulas
To convert mph to ft/s in a spreadsheet, put the mph values in column A and type =A2*22/15 in column B. For the reverse, =B2*15/22. The fraction is exact, so the cells carry no rounding error, and the formula works in all spreadsheet programs.
More values for convert mph 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 mph = 0.146667 ft/s
- 0.5 mph = 0.733333 ft/s
- 3 mph = 4.4 ft/s
- 4 mph = 5.86667 ft/s
- 7 mph = 10.2667 ft/s
- 15 mph = 22 ft/s
- 20 mph = 29.3333 ft/s
- 75 mph = 110 ft/s
- 200 mph = 293.333 ft/s
- 500 mph = 733.333 ft/s
- 2,000 mph = 2,933.33 ft/s
- 10,000 mph = 14,666.7 ft/s
Common slips when you convert mph to ft/s
The direction of the multiplication
If 60 mph turned into 41, you multiplied by 0.6818 instead of 1.4667. From mph to ft/s the number grows, and 60 mph is exactly 88 ft/s.
Reading mph as ft/s
An aeroplane lifting off at 60 mph is not lifting off at 60 ft/s. The error of nearly 47 per cent more than doubles the calculated take-off distance.
Rounding too early
If the speed will be squared in a performance formula, keep the decimals until the end.
Quick questions
What is the formula to convert mph to ft/s?
Feet per second equals miles per hour times 1.4667.
What is 60 mph in feet per second?
Exactly 88 ft/s.
What is 100 mph in feet per second?
146.67 ft/s.
What is one foot per second in mph?
0.6818 mph.
Is anything uploaded?
No, all calculations stay in your browser.
Related pages
Other speed converters are listed here: Convert mph to m/s, Convert mph to knots, Convert km/h to ft/s, Convert m/s 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. If you need the opposite direction, go to Convert ft/s to mph.
Remember the essentials: 1.4667 turns mph into ft/s, 88 ft/s equals 60 mph exactly, and the unit always travels with the number. Everything you type is handled by your own browser.