Online Stopwatch

About the Online Stopwatch

Use this online stopwatch whenever you need to time something precisely: running, swimming, rehearsing a talk or a lab experiment. Each time you press Lap, the time for that lap (the split) and the total time since the start are added to the table. With two or more laps, the fastest lap turns green and the slowest red.

Time is measured with the browser’s high-resolution clock (performance.now), so switching tabs or a screen that briefly turns off doesn’t introduce errors. Even if you reload the page by accident, your laps and the running time carry on.

How to use

1. Press Start. Time runs in hundredths of a second.
2. Press Lap at the end of each lap or segment. The lap time and total time are added to the table below.
3. Stop pauses the stopwatch and Resume continues. While stopped, Reset clears everything.
4. Copy laps copies the table so you can paste it into a spreadsheet or notes app.
5. On a computer, use Space (start/stop), L (lap), R (reset) and F (full screen).

Lap time vs. total time

The lap time (split) is the time from the previous lap to this one; the total time is the cumulative time from the start up to the moment you pressed Lap. For example, three laps of a 400 m track would look like this:

Here lap 3 is the fastest and lap 2 the slowest. The more even your lap times, the better your pacing.

Tips for accurate timing

• Human reaction time when pressing a button is typically 0.15–0.25 seconds. The 1/100 display is exact for the device, but hand timing always carries that reaction error.
• When comparing several people, have one person time everyone the same way (start exactly on the signal).
• To count down instead, use a timer; to alternate work and rest, use an interval timer.