How to use the Stopwatch
- Press Start, tap the time display or press the Space bar to begin timing.
- Press Lap or the L key each time a lap, rep or segment ends.
- Press Stop (or Space) to pause, then Resume to continue from the same time.
- Review the laps table, download it as CSV if you need it, and press Reset or R to start over.
Features
- Hundredth-of-a-second display driven by a high-resolution clock
- Unlimited laps with lap time and cumulative split time
- Fastest and slowest laps highlighted automatically
- Keyboard shortcuts: Space, L and R
- Keeps running through a page reload or accidental tab close
- Fullscreen mode and CSV export of your laps
Lap time versus split time
A stopwatch with laps gives you two numbers for every segment, and it helps to know which is which. The lap time is how long that segment alone took, from the previous lap press to this one. The split time (shown here as Total) is the running time from the very start up to that press. Coaches and runners use both: lap times show pacing, while splits show whether you are on track for a target finish.
Worked example
Suppose you run four 400-meter laps and press Lap at 1:32.40, 3:06.10, 4:41.95 and 6:12.40. The lap times are 1:32.40, 1:33.70, 1:35.85 and 1:30.45. The fourth lap is fastest and the third is slowest, so the table highlights them in green and red. The average lap is the final split divided by the number of laps: 6:12.40 ÷ 4 = 1:33.10.
| Lap | Lap time | Split (total) |
|---|---|---|
| 1 | 1:32.40 | 1:32.40 |
| 2 | 1:33.70 | 3:06.10 |
| 3 | 1:35.85 | 4:41.95 |
| 4 | 1:30.45 | 6:12.40 |
How accurate is an online stopwatch?
This stopwatch reads your browser’s high-resolution clock (performance.now()), which measures elapsed time in fractions of a millisecond and is not affected by changes to your computer’s wall clock. The display refreshes with every screen frame, typically 60 times per second, and shows hundredths. The time itself never drifts, because it is always calculated from the moment you pressed Start rather than by adding up small ticks. In practice the limiting factor is human reaction time when pressing the button, which is usually around 0.2 seconds, so for sport timing treat the last digit as approximate.
If you reload the page or the browser closes the tab, the stopwatch restores itself from the start time saved on your device and carries on. Laps are kept too.
Keyboard shortcuts
- Space starts, stops and resumes.
- L records a lap while running.
- R resets the time and clears the laps.
Shortcuts are ignored while you are typing in a text box, so they will not interfere with other parts of the page.
Ideas for using it
- Interval training, swimming lengths and track laps.
- Timing speeches, presentations and reading practice.
- Measuring how long tasks take, for estimates and timesheets.
- Science experiments and classroom activities, shown in fullscreen on a projector.
Need to count down instead? Use the Countdown Timer, or structure work and breaks with the Pomodoro Timer.
Frequently asked questions
Does the stopwatch keep running if I switch tabs?
Yes. Time is calculated from when you pressed Start, so switching tabs, locking your phone or reloading the page does not stop or slow it down.
What is the difference between lap and split?
Lap time is the duration of one segment. Split time is the total elapsed time from the start to the end of that segment. Both are shown for every lap.
How precise is it?
It uses a high-resolution clock and shows hundredths of a second. The real limit is how quickly you can press the button, so for official sport timing use dedicated equipment.
Can I save my lap times?
Click Download CSV to save all laps as a spreadsheet file. Laps are also kept in your browser until you press Reset.