Stopwatch & Timer

How to use the stopwatch and timer

1. Stopwatch: press Start to begin counting, Lap to record a split without stopping, and Stop to pause. Resume continues from where it stopped, and Reset clears everything. On a computer, the space bar starts and stops it, and L records a lap.
2. Timer: set hours, minutes and seconds, or tap a preset such as 5 min or 30 min, then press Start. Pause and resume at any time, add a minute if you need longer, and Reset to go back.
3. When a timer finishes it plays three beeps, repeats the beeps every two seconds up to eight times, and shows "Time's up!" under the clock and changes the page title to "Time is up" so you can notice it from another tab. Press Stop alarm to silence it.

Both tools run on your device's clock and do not need an internet connection once the page has loaded.

How laps work

A lap is a split time, the time since the previous lap (or since the start for the first one). The table shows two columns: the lap time for that segment and the running total. With three or more laps, the fastest and slowest are labelled so you can see how consistent you are.

lap time = total at this lap − total at the previous lap Example: totals of 1:05.20, 2:08.90, 3:15.00 give laps of 1:05.20, 1:03.70 and 1:06.10

The fastest lap here is the second (1:03.70) and the slowest the third (1:06.10). Pressing Lap does not stop the main clock, so your total time stays true however many laps you record.

Accuracy of the display

The stopwatch reads a high-resolution browser clock (performance.now()) and works out the time from the moment you pressed Start, rather than adding up the screen refreshes. If the tab is slow or hidden, the display may skip, but the time is never lost. The numbers are shown to a hundredth of a second, though the real accuracy is limited by your screen, which refreshes every 8 to 17 milliseconds, and by how fast you press a button. Human reaction time of about 0.2 seconds is the biggest source of error in hand timing.

The timer uses the wall-clock time, so it stays correct when a laptop sleeps or the tab is in the background. If you close the tab or lock a phone, mobile browsers may stop playing sound, so keep the page open for important alarms.

Common timer settings

The Pomodoro technique alternates 25 minutes of focused work with 5-minute breaks, and a longer break after four rounds. Set the timer to 25 minutes, and when it rings, set 5.

Getting the most from the stopwatch

• Running or swimming: press Lap at each lap of the track or pool, then copy the laps into a spreadsheet to see whether you slow down towards the end.
• Cooking and baking: use the timer for the recipe time and add a minute if the dish needs longer, without losing the countdown.
• Study sessions: time yourself per question to get an idea of your pace before an exam, and compare against the time allowed per question.
• Presentations: rehearse with the stopwatch and note the lap at each slide, so you know where you gain or lose time.

Averaging your laps is simple: divide the final total by the number of laps. For example, 4 laps in 5:20.00 is 320 seconds ÷ 4 = 80 seconds, or 1:20.00 per lap.

Accuracy and limits

The stopwatch keeps counting for as long as the page stays open; the timer counts down from up to 99 hours, 59 minutes, 59 seconds. Sound needs your browser to allow audio after a click, and phones in silent mode or with the screen locked may not play it. Neither tool keeps running if the page is closed or reloaded. Do not rely on it for safety-critical or medical timing.

Frequently asked questions