How to Convert MPH to Feet Per Second Squared

Remember that perception time and reaction time also affect braking distance -- how much ground a vehicle travels before it can fully stop.

Though vehicles often move fast enough for you to use the unit of miles per hour, several units can describe acceleration. Advertisers often specify acceleration informally as mph per second. A car, for instance, may accelerate from stationary to 60 mph in 4 seconds, giving an average acceleration of 15 mph per second. You can also calculate acceleration in feet per second squared, an alternate unit, from the speed that a vehicle reaches during a length of time.

Instructions

1. Multiply the vehicle's rise in speed, measured in miles per hour, by 5,280 to convert it to feet per hour. For example, if the car accelerates by 60 mph, 60 x 5,280 = 316,800 ft/h.

2. Divide this answer by 3,600, which is the number of seconds in an hour, to convert it to feet per second -- 316,800 / 3,600 = 88 ft/s.

3. Divide this answer by the time the vehicle takes to accelerate. For example, if the vehicle takes 4 seconds to accelerate, 88/4 = 22 feet per second squared.

References

• Rochester Institute of Technology: Displacement, Velocity, Acceleration
• Iowa State University: Agricultural Measurements and Conversions

Resources

• University of California: Car Performance Calculator
• Davidson College: An Accelerating Car