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Online stopwatch

Start, stop and record laps, accurate to a hundredth of a second.

How Online stopwatch works

Online Stopwatch measures elapsed time with millisecond precision and lets you record individual lap times during a session. Each lap captures the split time since the last lap as well as the total elapsed time, giving you both the individual segment duration and the cumulative running total. The stopwatch runs purely in the browser using the Performance API for timing; nothing is transmitted to any server and the tool works fully offline.

The Performance API provides higher-resolution timestamps than the standard Date API, allowing the display to update accurately to the millisecond. Lap data and the running state are written to your browser local storage as you go, so an accidental refresh or a closed tab does not lose the recording. Nothing leaves the device and no cookie is set; the reset control clears the laps.

Written by Bastien Sulyan

How to use Online stopwatch, step by step

  1. Click start to begin measuring elapsed time.
  2. Click lap at each checkpoint to record a split time without stopping the clock.
  3. Click stop to pause the timer while keeping your current time and laps.
  4. Click reset to clear the elapsed time and all recorded laps.
  5. Copy the lap table if you want the results outside the browser; they survive a refresh on their own.

Common use cases

  • A coach times individual swimming laps during practice, pressing lap at each turn to compare split times across the session.
  • A runner tests a new route segment by segment, recording each km split to identify where pace drops.
  • A quality-assurance tester times how long each step of a manual test protocol takes, using lap to separate each step.
  • A teacher conducts a reading comprehension test and uses the stopwatch to record when each student finishes their section.

Frequently asked questions

How precise is the stopwatch?

The stopwatch uses the browser's Performance API, which provides timestamps with sub-millisecond resolution on most devices. Display updates happen every 10-50 milliseconds depending on the browser. For practical purposes the displayed milliseconds are accurate; for scientific-grade timing, a dedicated hardware instrument is more appropriate.

Does the stopwatch continue if I switch browser tabs?

The underlying performance timestamp is not affected by tab switching because it references a monotonic clock. The visual display may update less frequently when the tab is in the background, but when you return to the tab the elapsed time shown will be accurate.

Are my lap times saved anywhere?

Lap times and the running state are saved in your browser's local storage, so an accidental refresh or a closed tab does not lose your recording. Nothing is sent to any server and no cookie is set. Use the reset control to clear the laps, or clear this site's data in your browser settings to remove the stored state entirely.

Is there a limit to how many laps I can record?

There is no enforced limit. Laps are kept in a JavaScript array and mirrored to local storage; you can record as many as your use case requires. For very large numbers of laps, the list scrolls rather than truncating.

Can I export the lap times to a spreadsheet?

The current tool does not have a built-in export button. You can select and copy the lap table from the screen and paste it into a spreadsheet. The rows are structured consistently so column alignment after pasting is straightforward.