Stopwatch

How to use the stopwatch

1. Click Start (or press the Space bar) to start timing. The elapsed time is shown to the hundredth of a second, and in the title of the browser tab.
2. Click Lap (or press L) each time a runner passes, a round ends or a task is finished. Each lap appears in the table with its Lap time, its Difference with the previous lap and its Split (total).
3. Click Stop (or press Space again) to pause. Resume continues from the same time.
4. When the stopwatch is stopped, Reset (or R) clears the time and the laps.
5. Click Export laps (CSV) to download the lap table and open it in a spreadsheet.

The keyboard shortcuts work anywhere on the page, except while you are typing in a field. If a button has the keyboard focus, the Space bar presses that button, as usual.

Lap time or split time?

The two numbers answer different questions:

• The lap time is the time of one lap only: from the previous lap press to this one. It shows your pace, lap by lap.
• The split time (shown as Split (total)) is the total time from the start to this lap press. It is what a coach reads out at each checkpoint.

For example, if you press Lap at 01:02.40 and then at 02:01.90, the second lap time is 59.50 seconds and its split is 02:01.90. The Difference column compares each lap with the previous one: a minus sign means the lap was faster. Once you have at least two laps, the fastest and slowest laps are marked, and the line above the table gives the number of laps and the average lap time.

Accurate even in the background

This stopwatch doesn’t count screen refreshes or timer ticks, which browsers slow down in background tabs. It stores the moment you pressed Start using the browser’s high-resolution monotonic clock (performance.now()), and computes the elapsed time from it each time the display is refreshed. So you can switch tabs or apps and come back later: the time stays exact, and a change of the computer’s clock (daylight saving time, network time sync) has no effect.

Two limits to keep in mind: closing or reloading the tab loses the time and the laps, and the display shows hundredths of a second, but your reaction time when pressing a key or a button is usually around 0.1 to 0.2 second. For official timing, use dedicated equipment.

The CSV file

The exported file has one line per lap with five columns: lap number, lap time and split time (formatted as minutes:seconds.hundredths), then the lap and split in raw milliseconds. The millisecond columns are easy to sort, add up or chart in a spreadsheet.