Calculators & Time

Online Stopwatch

A precise browser stopwatch that stays accurate even if you switch tabs, with full lap-time tracking.

Free & unlimitedRuns in your browserNo sign-up required

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About Chronometers and Precision Timing

A chronometer is a timekeeping device designed for precision measurement of elapsed time. In the digital context, browser-based timers use the JavaScript performance and Date APIs for sub-millisecond precision.

requestAnimationFrame for smooth updates

This timer uses requestAnimationFrame (rAF) for display updates, which synchronizes with the monitor's refresh rate (typically 60Hz). This avoids the timer drift that occurs with setInterval, which can accumulate errors of hundreds of milliseconds over a long session.

Lap timing in athletics

Lap timers were originally developed for track athletics to record split times between checkpoints. In software, the same concept is used for performance profiling — measuring how long each segment of a process takes relative to the total execution time.

Browser timer accuracy limits

Modern browsers intentionally reduce timer precision to mitigate Spectre-class side-channel attacks. Firefox reduces resolution to 1ms; Chrome to ~0.1ms in secure contexts. For production benchmarking, use performance.now() in a Node.js environment where microsecond precision is available.

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How it works

Three steps, no setup

Press start

Timing begins immediately with centisecond precision.

Pause, resume, or lap

Record lap splits without interrupting the running total.

Review your laps

Every recorded lap stays listed for the session.

Common questions

Frequently asked questions

Does it stay accurate if I switch tabs?

Yes, timing is calculated from real wall-clock timestamps rather than a naive interval counter, so it does not drift when the tab is backgrounded.

Is there a maximum time limit?

No practical limit — it will keep timing accurately for hours if needed.

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Calculators & Time

Online Stopwatch

About Chronometers and Precision Timing

requestAnimationFrame for smooth updates

Lap timing in athletics

Browser timer accuracy limits

Three steps, no setup

Press start

Pause, resume, or lap

Review your laps

Frequently asked questions

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About Chronometers and Precision Timing

requestAnimationFrame for smooth updates

Lap timing in athletics

Browser timer accuracy limits