A precise online stopwatch with millisecond accuracy and lap recording. Great for timing activities, workouts, or any event. Runs entirely in your browser.
A stopwatch is a precision timing tool used across sports, science, cooking, productivity, and education. Athletes time sprints and intervals, scientists measure reaction times, and productivity enthusiasts use the Pomodoro technique with timed work sessions. This browser-based stopwatch offers millisecond precision, lap timing for tracking splits, and a clean interface that works on any device. Unlike phone stopwatch apps, it runs in a browser tab — useful when your phone is being used for something else, or when timing activities on a computer. The timer uses requestAnimationFrame for smooth display updates and performance.now() for accurate time measurement, ensuring precision even when the browser tab is in the background.
It uses the browser's high-resolution timer (performance.now()), which provides sub-millisecond accuracy. The main source of imprecision is human reaction time when clicking Start/Stop, typically 150-250ms.
The display may not update when the tab is hidden (browsers throttle background tabs), but the timer continues running accurately. When you return to the tab, the correct elapsed time is shown.
Laps record intermediate times without stopping the overall timer. Runners use them for each track lap, swimmers for each length, and coaches to compare split performance across training sessions.
This tool provides a single stopwatch. To time multiple activities simultaneously, open multiple browser tabs each with their own stopwatch instance.
There's no practical limit — the stopwatch can run for hours or even days. It uses JavaScript's number precision, which can accurately represent time intervals well beyond any practical use case.