Online Stopwatch
Millisecond-precision stopwatch with laps — runs in your browser tab.
Free · No sign-up · Runs locally in your browser · Also available in Chinese (中文)
What is Online Stopwatch?
An online stopwatch measures elapsed time from start to stop, with lap times captured along the way. It uses your browser's monotonic clock rather than wall-clock subtraction, so background throttling and small wall-clock adjustments do not corrupt the count.
Laps are the feature that matters for real training and testing: each lap records its own duration plus the running total, so you can compare segment times without mental arithmetic. The display updates via requestAnimationFrame for a smooth readout that costs almost nothing to run.
How to use it
- 1Click start (or press Space) to begin timing.
- 2Press lap at each milestone — each lap's duration and cumulative total are recorded.
- 3Stop to freeze the timer; resume continues from the same value.
- 4Reset clears the count and the lap table.
Common use cases
- Timing sets and rest intervals during workouts.
- Measuring how long steps of a process take before writing documentation.
- Classroom timing for quizzes and speaking practice.
Frequently asked questions
▸What happens if I switch tabs?
Timing continues correctly because it is based on the monotonic clock — the display may pause while hidden but the elapsed value stays accurate.
▸How precise is it?
The display shows centiseconds; underlying precision is the browser's high-resolution timer, well beyond what the display shows.