Ball speed from video: shot, serve and throw

An online tool that measures ball speed from video — an alternative to a radar gun. Tap the ball and the track is found for you; the scale comes from court markings, from the flight arc, or from start and finish marks over a known distance. Slow motion is accounted for, and the result is printed with its error.

How to measure

Film from the side

Phone still, flight across the frame, ideally in slow motion.

Tap the ball

White boxes show what is moving; the track builds itself.

Set the scale

A line along the markings, the flight arc, or start and finish marks — and the speed is ready.

Find out how fast a shot, serve or throw was with an ordinary phone

Video of the shot or throwShot on a phone, slow motion is best

No video

How to film for an honest number

From the side, across the frame
Phone held still
Slow motion
Something of known length in view
Good light, contrasting ball

Speed

Upload a video — the speed and its error will appear here.

Ball speed from video

What is actually computed

The difference of three neighboring frames shows what moved; connected regions separate the ball from everything else. A straight line is fitted through the track — the speed is its slope, converted to meters by the frame scale, over every frame of the track rather than two. With marks, the speed is the distance divided by the time between two frames, and the error comes from the length of one frame.

What the tool does not do

It is not a radar. A track is honest only for motion across the frame and with a scale in that same plane; a ball flying at the camera reads low, and a warning says so. Air drag is not modeled — what is shown is the average speed over the stretch.

MP4 video: the flight with the track drawn on and the number on screen — for a coach or for sharing.

Features

One tap and the track is there

Tap the ball on any frame: tracking runs forwards and backwards by itself, taking at each step the region nearest the predicted position rather than the previous one — otherwise, for a fast ball, the nearest thing is the background.

Three ways to turn pixels into meters

A line along the markings, with ready sizes of goals, courts and pitches. The arc of free flight, with no ruler at all. Start and finish marks over a known distance — even when filmed from behind the server.

Slow motion does not fool it

A 240 fps clip often plays at 30, stretching its time eight times. The correction is one tap, and with both a line and an arc set the tool notices the mismatch itself and offers the slow-down.

A warning when the ball flies at the camera

A ball heading for the lens covers few pixels on screen, and the speed reads several times low. The clue is that the ball grows along the track; that growth is measured and stated in percent.

A series of attempts with the best one marked

Save measurements under a name: attempts gather in a table with a star on the best, and go out as CSV and as a PDF report with the frame and the drawn track.

A clip with the track and the number

With Premium the flight is rendered to MP4: the track is drawn over the frames and the speed stays on screen — a ready clip for a coach or social media.

Questions and answers

How accurate is this compared with a radar gun?

Three things set the accuracy, and all three are visible on screen. The scale: an error in the length of the line passes into the speed one for one, so take a long line in the plane of flight. The number of frames in the track: the more there are, the narrower the spread, and that spread is printed next to the number. The camera angle: with flight towards the camera the reading can be several times low. A radar has none of these weaknesses — but it has to be bought and carried to the field, while the phone is already with you.

What if I filmed from behind, or straight towards the ball?

A frame-by-frame track from that angle reads several times low — the ball barely moves on screen. Switch to “Marks”: mark the frame where the ball left the hand or racket and the frame where it crossed a known line, then type the distance (for example 18.44 m from the pitching rubber to home plate). The distance is measured on the field, not on the screen, so the angle stops mattering.

I filmed in slow motion. What should I set?

How many times the file is slowed down: 240 fps played back at 30 is 8×, 120 at 30 is 4×. If the file honestly carries 240 fps (some cameras record it that way), the slow-down is 1× — check the frame rate shown on the frame. When both a line and the flight arc are set, the tool notices stretched time by itself and offers the correction.

What is scale from the flight arc?

For a ball in free flight the vertical part of the path is a parabola, and its coefficient on time squared equals half the acceleration of gravity. Gravity is known, so the parabola tells how many meters go into one pixel — no ruler in the frame is needed. It works only for genuine free flight: a rolling ball has no such parabola.

The ball is not picked up when I tap it. What now?

Most likely it is not yet flying in that frame, or it is at the edge. Step through the frames with the arrows: white boxes show everything that moves. If there are no boxes, the motion is too small — move closer or film in slow motion, or mark start and finish by hand. A ball half out of the frame is deliberately left out of the track: its center is pulled inwards and would drag the speed down.

Is air drag taken into account?

No. A straight line is fitted through the track, so what is shown is the average speed over that stretch. For a ball that slows noticeably, the speed right after contact is higher than the average, and the gap grows with the length of the track. For launch speed, take a short track right after contact.

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Who is this tool for?

🏃 Sports & Athletics

Published 12 Sep 2026 Updated 15 Sep 2026 Author: The Supreme