Feet per Second vs Miles per Hour: Speed Conversions

A speed conversion is two conversions stacked: one for distance and one for time. To turn feet per second into miles per hour you multiply by 3,600 to get feet per hour, then divide by 5,280 to get miles per hour.

Combine them and you get a single factor of 3,600 ÷ 5,280 = 0.681818…, a repeating decimal. Its reciprocal, 5,280 ÷ 3,600 = 1.466667…, converts the other way.

Neither has a clean decimal form, which is why good converters hold the fraction and round only at the end. Doing it the other way is how you end up with 60 mph coming out as 87.9998 ft/s.

60 mph is exactly 88 ft/s, and it is worth memorising because it makes every multiple easy: 30 mph is 44 ft/s, 15 mph is 22 ft/s, 120 mph is 176 ft/s.

It also makes reaction distance intuitive. At 60 mph a car covers 88 feet every second. A typical driver reaction time of 1.5 seconds is 132 feet — most of a football field — before the brakes are even applied.

That is the practical reason this conversion appears in driver training. Speed in mph is abstract; speed in feet per second is the distance you travel while deciding what to do.

Going the other way, miles to feet does the reverse conversion. If you want a figure already worked out, conversion chart lists the common ones, and about & methodology documents every constant used here and where it comes from.

For mph to ft/s, multiply by 1.5 and subtract a little. 70 mph × 1.5 = 105, and the true answer is 102.7. That is within 2.5%, which is fine for an estimate.

For ft/s to mph, multiply by two-thirds. 100 ft/s × 0.67 = 67, against a true 68.2. Also within 2%.

For precision — ballistics tables, physics homework, engineering specs — use the exact factors. The approximations are for judging whether an answer is plausible, not for producing one.

Feet per second dominates where the timescale is short: ballistics, impact testing, sprint biomechanics, machine feed rates, fluid velocity. Anything measured over a second or less.

Miles per hour dominates where the timescale is long: vehicles, wind, weather. Anything you would sustain for minutes.

The unit tells you something about the question. A number in ft/s usually accompanies an event; a number in mph usually accompanies a journey.

Here is why 88 ft/s is genuinely useful. At 60 mph you travel 88 feet every second. Typical human reaction time is about 1.5 seconds — so before your foot even reaches the brake, you have covered 132 feet.

Add the actual braking distance, which on dry tarmac from 60 mph is roughly 120 to 140 feet for an average car. The total is about 260 feet — more than two basketball courts, or roughly 0.05 miles.

At 30 mph (44 ft/s) everything shrinks sharply: about 66 feet of reaction and about 35 feet of braking, 100 in total. Doubling your speed does not double the stopping distance — it roughly triples it, because braking distance grows with the square of speed.

That is the sort of thing which is invisible in mph and obvious in feet per second. The unit you choose changes what you notice.

If you are working in physics or engineering, metres per second is usually better — not because it is more accurate, but because the units stay consistent across the whole calculation.

In SI, gravity is 9.81 m/s², energy is in joules and force is in newtons. There is no conversion factor in the middle of anything. In imperial, gravity is 32.2 ft/s² and mass carries its own complications in slugs and pound-mass.

The conversion is simple: 1 ft/s is 0.3048 m/s, and 1 m/s is 3.28084 ft/s. So 88 ft/s is 26.82 m/s, and 10 m/s is 32.8 ft/s or 22.4 mph.

Related conversions: nautical miles for speed, sq ft to sq miles for land area, and feet to mil for the unit people most often confuse with the mile.

In sport, a fast sprinter peaks at about 37 ft/s (25 mph). A fast baseball pitch is about 147 ft/s (100 mph). A badminton smash can reach 480 ft/s.

In nature, a 90 mph storm is 132 ft/s. Sound is 1,116 ft/s. Light is about 983 million ft/s — a number so large that nobody uses feet for it.

The point of the list is not the figures but the range. The same unit spans a human walk and an aircraft, and converting to mph across that entire range is one multiplication by 15/22. That is the advantage of a unit built from exact whole numbers.