Online stopwatch

This online stopwatch starts with one click on Start or a tap of the space bar: time runs straight away in minutes, seconds and hundredths, then in hours after 59 minutes. While it runs, Lap (or the T key) records a split, and the table on the right shows each lap time and the running total since the start. For example, on an 8 × 400 m interval session at a running track, the eight laps line up, the fastest turns green and the slowest orange, so you see at a glance whether your pace is dropping. Pause freezes the time without clearing it, and Reset goes back to 00:00.00. The reading stays correct if you switch tabs or your screen locks, because it relies on the device clock. The main limit is you: pressing with a finger adds 0.15 to 0.25 seconds of reaction time, which rules it out for official race timing.

Click Start and the time runs in minutes, seconds and hundredths. Pause freezes the display without clearing anything, and Resume carries on from there. During the run, Lap records a split: the table shows that lap's duration and the total, and highlights the fastest and slowest laps once there are two. Reset only works while the stopwatch is stopped, so a stray click cannot wipe a measurement. Copy laps puts the list on your clipboard, ready to paste into a spreadsheet.

Full screen enlarges the digits so you can read them from the back of a room or from a treadmill; press Esc to leave. On an iPhone, Safari only allows full screen for videos: turn the phone sideways and the digits fill the width instead.

Running and gym sessions: interval laps on a track, planks, rest between sets. The lap times show immediately when you start to slow down, whether you train at a municipal stadium or in a park.

Presentations and interviews: rehearsing a 10-minute talk or a 3-minute pitch, recording a lap at each part to see which one runs over. That helps if you prepare an oral exam in French, such as the DELF or a naturalisation interview. When the duration is fixed and you want an alarm, the online timer with an alarm suits better, because it counts down.

Classroom experiments, cooking and games: the time an object takes to fall, a reaction, a round of a board game. For a dated event such as a flight home or an exam, the countdown to a date shows the days left.

A web stopwatch that added one hundredth every 10 milliseconds would soon drift: browsers slow down timers in background tabs, and Chrome, after five minutes in a hidden and silent tab, runs some of them only once a minute. This stopwatch works differently. At the start it notes the exact device time, to the millisecond. On every frame it recalculates the gap between now and that moment, plus the time banked before the last pause. The display may jump when the tab comes back to the front, but no time is lost.

Why the device clock rather than the browser's high-resolution clock (performance.now)? On some systems that clock stops while the device sleeps, so a phone that locks its screen would lose those minutes. The device clock always moves on. The trade-off: if the computer clock is corrected during a measurement (network time sync), the timed result moves by the same amount, which is rare and at most around a second.

• BIPM, SI base unit: second (s), page read on 27 October 2026.
• W3C, High Resolution Time, page read on 27 October 2026.
• WHATWG, HTML Standard, Timers, page read on 27 October 2026.
• WHATWG, Fullscreen API Standard, page read on 27 October 2026.
• Chrome for Developers, Heavy throttling of chained JS timers beginning in Chrome 88, page read on 27 October 2026.

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