Tennis Serve Speed Calculator
Turning a Stopwatch Into a Radar Gun
Broadcast radar guns give serve speed instantly, but the same number can be recovered with nothing more than a known distance and a timer. If you know how far the ball traveled and how long it took to get there, average speed follows directly from basic kinematics. This calculator applies that relationship, converting a measured flight time into a serve speed reading in either kilometers per hour or miles per hour.
The Formula
The calculation reduces distance and time to a single average-speed figure:
Speed (m/s) = Distance (m) ÷ Time (seconds)
Speed (km/h) = Speed (m/s) × 3.6
Speed (mph) = Speed (m/s) × 2.2369362921
The default flight distance is 18.4 meters (about 60 feet), which the calculator uses if no distance is supplied. Any other measured distance — from a court marking, a video frame count, or a laser measurement — can be substituted directly.
Where This Calculation Is Useful
- Practice courts without radar — a phone camera's frame rate or a simple stopwatch can substitute for a speed gun once distance is fixed.
- Coaching feedback — tracking flight time across a training session gives a consistent, repeatable speed estimate without dedicated equipment.
- Cross-checking radar readings — comparing a timed estimate against a gun reading helps catch equipment or angle errors.
- Video analysis — frame-by-frame review of recorded serves converts naturally into a time value this calculator can use.
Speed at Different Flight Times
Holding the default 18.4-meter distance constant, small changes in flight time produce large swings in computed speed, since speed and time are inversely related:
| Flight time | Speed (km/h) | Speed (mph) |
|---|---|---|
| 0.35 s | 189.3 | 117.6 |
| 0.40 s | 165.6 | 102.9 |
| 0.45 s | 147.2 | 91.5 |
| 0.50 s | 132.5 | 82.3 |
| 0.55 s | 120.4 | 74.8 |
| 0.60 s | 110.4 | 68.6 |
Figures above are computed directly from this calculator's own formula at the default 18.4 m distance; they reflect average speed over the full flight, not the peak speed a radar gun captures near the racket.
How to Use This Calculator
- Enter the flight Distance, or leave it at the default of 18.4.
- Choose the distance unit — Meters or Feet.
- Enter the Time in seconds it took the ball to cover that distance.
- Choose the speed unit for the result — km/h or mph.
- Select Calculate to get the computed serve speed.
Related Calculations
For overall on-court performance tracking, see the Tennis Elo Rating Calculator, which turns match results into a skill rating over time.