What Is Feet per Second (ft/s)?
Feet per second, written as ft/s, is a unit that measures speed. It tells you how many feet something moves in one second. If a ball moves 10 ft/s, it travels 10 feet every second.
Definition
Feet per second is the speed of an object that moves a certain number of feet during one second of time.
In simple form:
Speed in ft/s = distance in feet divided by time in seconds
So, if you run 30 feet in 3 seconds:
- Speed = 30 feet / 3 seconds = 10 ft/s
History / Origin
The unit feet per second comes from two older ideas:
- Foot comes from old measuring systems in England. It was based on the length of a human foot and later fixed carefully as 0.3048 meters.
- Second is a time unit used in clocks. It is part of the standard time system used all over the world.
When people started to study motion in physics and engineering, they needed a way to describe how fast something was moving. In English speaking countries that used feet, they naturally used feet per second to show speed. Later, the metric unit meters per second became more common in science, but feet per second is still used in many practical fields.
Symbol & Abbreviation
The usual short forms for feet per second are:
- ft/s
- ft sec-1 in some science texts
- Less common forms include fps or ft/sec, but ft/s is clearer.
All of these mean the same thing: the number of feet moved in one second.
Current Use Around the World
Feet per second is not the main speed unit everywhere, but it is still important in some areas:
- United States and some other countries using imperial units: used in engineering, building design, firefighting water flow, and some sports.
- Physics and engineering problems: sometimes use ft/s when other lengths are already given in feet.
- Sports and games: used to describe the speed of balls, runners, or projectiles where measurements are in feet.
- Ballistics and firearms: bullet speeds are often given in ft/s in catalogs and reports.
In science worldwide, meters per second (m/s) is more common, but ft/s is still very useful when working with imperial units.
Example Conversions
To use feet per second with other speed units, you often need to convert it. Here are common conversion rules in simple form.
Feet per Second to Meters per Second
1 foot is exactly 0.3048 meters.
Formula:
speed in m/s = speed in ft/s × 0.3048
Examples:
- 10 ft/s × 0.3048 = 3.048 m/s
- 30 ft/s × 0.3048 = 9.144 m/s
- 100 ft/s × 0.3048 = 30.48 m/s
Meters per Second to Feet per Second
1 meter is about 3.28084 feet.
Formula:
speed in ft/s = speed in m/s × 3.28084
Example:
- 5 m/s × 3.28084 ≈ 16.4 ft/s
Feet per Second to Miles per Hour (mph)
There are 5280 feet in 1 mile and 3600 seconds in 1 hour.
Formula:
speed in mph = speed in ft/s × 0.681818 (you can round to 0.682)
Examples:
- 10 ft/s × 0.682 ≈ 6.82 mph
- 20 ft/s × 0.682 ≈ 13.6 mph
- 44 ft/s × 0.682 ≈ 30 mph
Miles per Hour to Feet per Second
Formula:
speed in ft/s = speed in mph × 1.46667 (you can round to 1.47)
Examples:
- 30 mph × 1.47 ≈ 44 ft/s
- 60 mph × 1.47 ≈ 88 ft/s
Feet per Second to Feet per Minute
There are 60 seconds in 1 minute.
Formula:
speed in ft/min = speed in ft/s × 60
Example:
- 5 ft/s × 60 = 300 ft/min
Related Units
Feet per second is one of many units used to measure speed. Other related units include:
- Meters per second (m/s) the main speed unit in the metric system and in science.
- Kilometers per hour (km/h) common for road speeds on car speedometers.
- Miles per hour (mph) used for road speeds in the United States and some other countries.
- Feet per minute (ft/min) used for things like elevator speeds and air flow.
- Knots (nautical miles per hour) used in ships and airplanes.
All of these tell how far something moves in a certain time. They only differ in what length unit and time unit they use.
FAQs
What does feet per second actually measure?
Feet per second measures speed. It tells you how many feet an object moves during one second. More ft/s means something is moving faster.
Is ft/s the same as fps?
In speed and physics, yes, fps is often used as a short way to write feet per second. But in video and movies, fps can also mean frames per second, which is different. To avoid confusion, ft/s is the clearest symbol for speed.
Which is faster, 10 ft/s or 10 mph?
10 mph is faster. One mph is about 1.47 ft/s, so 10 mph is about 14.7 ft/s.
Why do scientists prefer m/s instead of ft/s?
Scientists use the metric system, which is the same worldwide. Meters and seconds are standard SI units, so using m/s makes it easy to share and compare results globally.
Where might I see speeds in feet per second in real life?
You might see ft/s in physics homework, engineering plans, gun and archery catalogs for bullet or arrow speeds, sports science reports, or building and safety codes that use feet.
How can I quickly estimate ft/s from mph in my head?
A quick method is: multiply mph by 1.5 to get a rough ft/s value. For example, 40 mph is about 40 × 1.5 = 60 ft/s. The exact value is slightly lower, about 58.7 ft/s.
Is feet per second an SI unit?
No. SI units are the official metric units. For speed, the SI unit is meters per second (m/s). Feet per second is from the imperial system, not from SI.
Can I use ft/s in school physics problems?
Yes, you can, as long as all the other length units in the problem are also in feet. If you mix units, you must convert them so they match before doing the math.