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Stopwatch

The Online Stopwatch is a precise, browser-based timer for measuring elapsed time with lap recording. Use it to time workouts, cooking, experiments, presentations, race splits, or any activity where you need accurate elapsed time with the ability to record intermediate times. No app or download required — runs entirely in your browser.

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About the Online Stopwatch

The Online Stopwatch is a precise, browser-based timer for measuring elapsed time with lap recording. Use it to time workouts, cooking, experiments, presentations, race splits, or any activity where you need accurate elapsed time with the ability to record intermediate times. No app or download required — runs entirely in your browser.

How to use it

  1. Click Start to begin timing.
  2. Click Lap to record split times without stopping the main timer.
  3. Click Stop to pause the stopwatch.
  4. Click Reset to return to zero and clear all lap times.

Formula & methodology

Elapsed time = current timestamp - start timestamp. Lap time = current lap timestamp - previous lap timestamp. Running average lap: sum of lap times / number of laps. Fastest/slowest lap: min/max of recorded lap times. Display: HH:MM:SS.ms format. Browser accuracy: performance.now() provides sub-millisecond precision.

Common use cases

  • Timing workout intervals or rest periods between sets
  • Recording lap times during running or cycling training
  • Timing presentations or speeches to hit duration targets
  • Cooking: timing multiple dishes simultaneously with laps
  • Testing and benchmarking: timing how long a process takes

Frequently asked questions

Modern browsers use performance.now() which provides resolution up to 0.1 milliseconds (though browsers may round to 1ms for security). For practical timing purposes (workouts, cooking, presentations), browser stopwatches are accurate to within a few milliseconds. For professional athletic timing requiring sub-10ms precision, dedicated hardware timers are more appropriate.
Yes — the stopwatch continues running in the background even when you switch tabs. However, some browsers throttle background tab timers to save battery. The elapsed time calculation uses timestamps rather than interval counting, so the displayed time remains accurate even if the display update slows. Return to the tab to see the current elapsed time.

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