Measure Feet Per Second, or Miles Per Hour

Simple way to measure fps using a camera and cardboard. your video camera takes a picture several times per second, if you know how fast id dose this then you can calculate speed my camera takes a picture 30 times per second (30 frames per second) if your camera is slower it will be less accurate and might not see projectile.
I shot my 180 fps airsoft gun and my camera got only 1frame of it. My 270 fps gun the camera did not see.
this is not to be judged in the launch it competition, its for the many people that could use this to improve their instructables
video on step 5

using some gestimation (fired sling shot and half way pulled back) i estimated the speed of my sling shot at 72 miles per hour (at full speed the camera didnt see any thing so i just multiplied by 2 i know its not accurate but it dosent have to be.)

the pics below:
it spent 4 frames on the lined part of board. after crunching the numbers the 14 gram projectile averaged 7.5fps (this is one of 5 tests) it was fired from my 7 gram torsion spring catapult

Step 1: Gather Materials

you will need:
a camera (at least 20 frames per second)
flat cardboard ( around 2 feet long 1 foot tall)
ruler (as long as cardboard is tall)
tape or thick marker (tape: blue scotch painters tape 1inch think)
calculator (recommended not needed)
tripod recommended

Step 2: Board Set Up

using a pencil and ruler mark 1 inch along the board
do the same for opposite side.

then draw a strait line across.

if using tape, tape right between the lines.

if using marker color between lines

if your board has little bit left over just put "spots" so you know its not a full inch

Step 3: Set Up.

I used a table vice to help hold card board in place (I didnt use the vice part of it through)
You could tape the board to a wall
I had to put a bucket of putt behind the board so it wouldnt tip over (I used putty because it was right sitting on the bench behind vice)

Keep in mind the angle of trajectory, catapults tend to fire at a high angle, sling shots k'nex guns airsoft guns Ect. Go relatively strait (duh)

Step 4: Set Up Camera and Projectile

you will need a tri-pod to get a good video

i used a heavy weight (2x as much as the catapult its self) this way it would go slower and would be easier to document for instructable.

Step 5: Fire/lanch/shoot/setoff/throw

After setting up tripod, set up the camera make sure its set to the highest frame rate possible.
Zoom in so you only see the board.
Get ready load/cock your weapon
Start filming, quickly fire your weapon into a safe backstop stop the camera
REPEAT 4+ times to rule out anomalies

Step 6: Computation

After you have taken the videos record the data
Go frame by frame in video,
1Count the number of frames the projectile flew over the board not the entire time its visible only when its on the marked part of board # will be referred to as A
2Record the distance the projectile flew over the board it should go strait across but the first test mine didnt # will be referred to as B
3And last, record how many inches it traveled in the fist frame # will be referred to as C

Now average every thing up so youre just working with the 1 set of what you did above. So you have one A, one B and, one C
The speed the camera records will be referred to D

The simple way I did this was CXD/12=Feet per second
EXSAMPLE 3X30=90 90/12=7.5=feetpersecond

So know you know approximately how fast it was traveling

Want to convert FPS to MPH?
Heres how
just multiply the fps by 0.6818 and your done!
want to convert to something else
check this out



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    29 Discussions


    1 year ago

    by the way I want to thank you for posting this instructable as I can't find out any where else where to find this info and I am doing some dhigh speed photography work now


    1 year ago

    I was curious what the "A" is for in the computations...."1Count the number of frames the projectile flew over the board not the entire time its visible only when its on the marked part of board # will be referred to as A"... what do y9u do with this number??? I can't see where yoiu use this number in your computations??


    Reply 10 years ago on Introduction

    touche or however the hell you spell that... what with the accent and stuff...

    Cat on my Lap

    11 years ago on Introduction

    The conversion isn't too hard, once you get one or the other side. Multiply f/s by 0.3048 to get m/s. Easy as pi.

    1 reply

    11 years ago on Introduction

    hey dude im trying to come up with a "standard" firepower idea that might be usefull to finding out the true power of a gun, what would you say the adverage of a normal blue rod shooting gun?, and one that fires through papper?


    11 years ago on Introduction

    If yoy wanted this to be for cm pper second or km per second would you just make the gaps 1 cm wide ir is there something else? great instructable


    11 years ago on Introduction

    Wow, I also wondered how the mythbusters do it. Although i'm too lazy to take the measurements and figure it out by my self. It's not all that hard.

    o, thats were i got it, i had this dream that i was using it to test some gun thing i made. next day i made this and i knew id seen it in the real world i just couldn't remember where. so yeah i guess i subconsciouly (sp) i did


    11 years ago on Introduction

    Yeah, I agree with oinkoinkzoopals, it really should be done with a high-speed camera, that way when you are done you can take a whole bunch of cool high-speed footage afterwards, like popping a water balloon, or dropping a water droplet. And don't you know that you are supposed to do math in pencil?

    1 reply

    that was pencil. origanly i had no plans of making an instructable so i didnt use a graph or bother with erasing cause it was for my dyslexic eyes only