Tennis serve speed calculator
Measure your serve from any phone video, no radar gun needed. Mark the frame you hit the ball and the frame it bounces; the calculator does the physics.
Speed is distance over time. The ball travels about 18.5 meters from contact to a bounce near the service line, so if your video shows that flight took 12 frames at 30 fps (0.4 seconds), the average speed was about 46 m/s (104 mph). Because air drag slows the ball on the way, its speed off the racket was higher; the calculator estimates that too.
Calculate your serve speed
Your video stays on your device. It's opened in this browser tab and never uploaded.
Choose a video, step to the frame where the racket meets the ball, mark contact, then step to the first frame the ball touches the court and mark the bounce.
How to get an accurate reading
- Film from the side, far enough back that both you and the service box are in frame. From behind, the bounce is hard to pin down.
- Use slow motion if you have it. At 30 fps one frame is a third of a tenth of a second, so being one frame off moves the result by about 7%. At 240 fps it's under 1%.
- Set the frame rate of the saved video. For a clip recorded at 240 fps and saved to play at 30 fps, select 30 fps and Slowed 8×. For a clip that plays at normal speed at 240 fps, select 240 fps and Normal speed.
- Mark the first frame of each event: the first frame the strings touch the ball, and the first frame the ball touches the court.
How the calculation works
The distance comes from the court's fixed dimensions in the ITF Rules of Tennis: the baseline is 11.89 m from the net and the service line 6.40 m beyond it, so a serve to the service line T travels about 18.3 m along the ground. The calculator measures from where a server usually stands, half a meter beside the center mark, to the spot you tapped on the court: wider serves travel further (the singles court is 8.23 m wide), and it adds the drop from a typical contact height of 2.5 m.
The average speed is that distance divided by the time between your two marks. The speed off the racket accounts for air drag, which slows a ball in proportion to the square of its speed. Using the drag coefficient measured for new tennis balls (about 0.51) and the ITF ball size and weight, a serve arrives at the bounce at roughly 70% of the speed it left the racket. That is why a radar gun, which reads the ball just after contact, shows a higher number than the average.
What this ignores: spin (which changes drag and the path slightly), gravity speeding the ball up as it drops, and wind. Treat the result as a good estimate, accurate to within the range shown, not a certified radar reading.
Want to know why it's that speed?
Speed comes from the motion behind it: leg drive, trunk rotation, and a relaxed arm through contact. Baseline watches your serve on video and writes up what's helping and what's costing you, with drills.
Upload the same clip to Baseline for a coaching report on your serve. The first analysis is free.
Sources
- ITF, Rules of Tennis (court dimensions, Rule 1; ball specification, Appendix I)
- Rod Cross and Crawford Lindsey, aerodynamics of tennis balls: drag coefficient of new balls 0.507 ± 0.024 (Tennis Warehouse University)
- Goodwill, Chin and Haake (2004), Aerodynamics of spinning and non-spinning tennis balls, J. Wind Eng. Ind. Aerodyn. 92
Related
- How to film your tennis: Where to put your phone, which angle to use, what frame rate and clip length work best, and the mistakes that make tennis video useless for analysis. A practical setup guide.
- What AI analysis can see: An honest look at AI tennis coaching from phone video: what it reads well, what it gets wrong (forehand vs backhand, spin), and how to use the feedback without overhauling your game.