What Is Feet per Second (ft/s)?
Feet per second is a unit for speed. It tells you how many feet an object travels during one second. If something moves at 1 ft/s, it covers one foot of distance in each second.
This unit is common in the United States and in subjects like physics, engineering and sports. It is very handy when distances are measured in feet and time in seconds.
Definition
Feet per second (ft/s) is the speed of an object that moves one foot of distance in one second of time.
More formally:
- Speed in ft/s = distance in feet divided by time in seconds.
Feet per second is a non metric unit. It is based on the foot from the Imperial and US Customary systems.
Using standard conversion for the foot:
- 1 foot = 0.3048 meter
- So 1 ft/s = 0.3048 meter per second (m/s)
This means if you know a speed in ft/s, you can quickly change it to meters per second by multiplying by 0.3048.
History / Origin
The unit feet per second grew from the older unit foot, which has been used for hundreds of years in Europe and later in North America. People first used body parts like a human foot to measure length. Over time the foot became more carefully defined so everyone could agree on the same size.
The modern foot is now fixed by an exact metric value.
- Since 1959 one international foot is exactly 0.3048 meter.
Once the foot was fixed, many related units appeared, such as feet per second for speed and feet per second squared for acceleration. Scientists and engineers used ft/s in older textbooks and technical work, especially in countries that used the Imperial system. Today most science uses meters per second, but ft/s still remains in many practical fields.
Symbol & Abbreviation
The most common short form for feet per second is:
- ft/s
You may also see:
- ft sec−1 often in physics formulas
- fps written in plain text. Be careful, fps is also used for frames per second in video and gaming, which is a different idea.
All of these try to show the same meaning. Distance in feet divided by time in seconds.
Current Use Around the World
Feet per second is not an official SI unit. Still, it is used in many real life situations, especially where feet are normal for distance.
Common uses include:
- Sports and athletics. Measuring the speed of runners, football players, baseball pitches or thrown objects.
- Engineering and construction. Describing water flow in pipes or open channels, some machinery speeds or moving parts.
- Ballistics and firearms. Bullet and arrow speeds are often given in feet per second.
- Theme parks and rides. Speeds of roller coasters and rides may be stated in ft/s for technical planning.
- Education. Physics and math problems in US schools often use ft/s.
However, in most of the world, and in high level science, the main speed unit is meters per second (m/s) or kilometers per hour (km/h). Even in the United States, public road speeds are usually given in miles per hour (mph) instead of ft/s.
Example Conversions
Below are useful rules and examples to convert feet per second into other popular speed units.
Key conversion factors
- 1 ft/s = 0.3048 m/s
- 1 ft/s ≈ 1.0973 km/h
- 1 ft/s ≈ 0.6818 mph
- 1 ft/s ≈ 0.5925 knots
Formulas
- ft/s to m/s: m/s = ft/s × 0.3048
- ft/s to km/h: km/h = ft/s × 1.09728
- ft/s to mph: mph = ft/s × 0.681818… (about 0.682)
- ft/s to knots: knots = ft/s × 0.592484… (about 0.592)
Sample conversion table
| Speed | m/s | km/h | mph | knots |
|---|---|---|---|---|
| 1 ft/s | 0.3048 | 1.10 | 0.68 | 0.59 |
| 5 ft/s | 1.524 | 5.49 | 3.41 | 2.96 |
| 10 ft/s | 3.048 | 10.97 | 6.82 | 5.92 |
| 30 ft/s | 9.144 | 32.92 | 20.45 | 17.77 |
| 100 ft/s | 30.48 | 109.73 | 68.18 | 59.25 |
Everyday comparisons
- A slow jog of about 4 mph is roughly 5.9 ft/s.
- A typical city car speed of 30 mph is about 44 ft/s.
- A strong baseball pitch at 90 mph is about 132 ft/s.
Related Units
Feet per second connects to many other speed and distance units.
Other speed units
- Meters per second (m/s) main SI speed unit. 1 ft/s = 0.3048 m/s.
- Kilometers per hour (km/h) common road speed unit in most countries. 1 ft/s ≈ 1.0973 km/h.
- Miles per hour (mph) common road speed unit in the US and UK. 1 ft/s ≈ 0.6818 mph.
- Knots (kt) used in ships and aircraft. 1 ft/s ≈ 0.5925 kt.
Length units
- Foot (ft) base length unit in ft/s. 1 foot = 0.3048 meter.
- Meter (m) base SI length unit. 1 m ≈ 3.28084 ft.
Time units
- Second (s) SI base unit of time and the time unit used in ft/s.
- Hour (h) used in units like km/h and mph. 1 hour = 3600 seconds.
Related physical quantities
- Feet per second squared (ft/s²) acceleration. Change of speed in feet per second each second.
- Frames per second (fps) not a speed of motion through space but speed of images in video and games. The same letters fps are used, but the meaning is different.
FAQs
Is feet per second an SI unit?
No. Feet per second is not an SI unit. It is based on the foot from the Imperial and US Customary systems. The SI unit for speed is meters per second (m/s). You can change ft/s to m/s using 1 ft/s = 0.3048 m/s.
How do I convert feet per second to miles per hour?
Use this simple rule:
- mph = ft/s × 0.6818
For example, 50 ft/s × 0.6818 ≈ 34.1 mph.
How do I convert feet per second to meters per second?
Multiply by 0.3048.
- m/s = ft/s × 0.3048
For example, 20 ft/s × 0.3048 = 6.096 m/s.
What is a typical walking speed in feet per second?
A normal walking speed is about 3 to 4 mph. This is roughly 4.4 to 5.9 ft/s. So if a person walks at 5 ft/s, they are walking quite fast.
Why do some sports use feet per second instead of miles per hour?
Sports like baseball or some track events deal with short distances on fields marked in feet. Feet per second connects more directly to those field markings and to timing over short distances. It can make calculations and diagrams simpler for coaches and engineers.
Is fps the same as feet per second?
Sometimes fps means feet per second, especially in ballistics tables. But fps is also widely used for frames per second in video, movies and games. You must look at the context. If the topic is motion of objects, fps probably means feet per second. If the topic is video or animation, fps means frames per second.
How fast is 100 ft/s in everyday terms?
100 ft/s is about 68 mph or 109.7 km/h. This is similar to the speed of a car driving on a highway. It is also a common speed for fast moving balls or projectiles in some sports and experiments.
Why is it useful to know feet per second if most people use mph or km/h?
Feet per second makes it easier to connect time, distance and speed in math and physics problems that use feet and seconds. It also helps engineers and technicians who work with equipment built using Imperial units. Knowing ft/s and how to convert it lets you understand a wider range of books, tools and data.