Online Stopwatch
Stopwatch online: press start or the space bar – record laps with “Lap” or the L key. For sports, cooking or rehearsing a speech: it keeps counting even after you reload the page.
Source: W3C: High Resolution Time (timing in the browser). Updated: .
How it is calculated
How the online stopwatch works
The stopwatch stores the start time and calculates the display from the difference to the current clock. It does not count on its own, so it never falls behind when the browser throttles a background tab. State and laps are saved in your browser (localStorage): after reloading or reopening the page, the measurement continues. In private browsing mode this is lost when the window closes.
How to use it in three steps
- Click Start or press Space – time runs in minutes, seconds and hundredths.
- For each split, click Lap or press L or Enter.
- Stop pauses the watch, “Resume” continues, “Reset” clears time and laps.
Example uses
- Sports & training: track lap times per length while swimming or per interval while running, then see the fastest/slowest lap at a glance.
- Cooking: time how long tea steeps, eggs boil, or dough rests, to the second.
- School and PE class: record sprint or relay times over several runs as laps, then copy them as a table.
- Rehearsing a speech: lap each section of a talk while practicing to hit your target time.
Lap time, total time and copying results
Lap time is the time since the previous lap, total the time since start. From two laps on, the fastest is marked green and the slowest red. “Copy laps” puts a tab-separated table on your clipboard, ready to paste into Excel or Google Sheets.
Example: three laps on a 400 m track with lap times of 1:42.35, 1:39.80 and 1:45.10 give totals of 1:42.35, 3:22.15 and 5:07.25. Lap 2 is the fastest (green), lap 3 the slowest (red); the gap is 5.30 seconds and the average lap 1:42.42.
Accuracy and limits
The display shows hundredths of a second (decimal point). The calculation itself is accurate to the millisecond, but real-world accuracy is limited by your reaction time when clicking or tapping, typically 0.1 to 0.3 seconds. A browser stopwatch is not suitable for official competition timing.
Tips for more accurate hand timing
- Use the keyboard (Space, L) – a key press is usually quicker and more consistent than aiming with the mouse.
- Have the same person start and stop on the same device: reaction time then applies at both ends and partly cancels out.
- React to a predictable event, such as a hand touching the pool wall, rather than waiting for a sound.
Embed it on your own website
The stopwatch is also available as an embeddable widget, for example for a club or school website – with laps, keyboard control and copy function just like here.
Share a result
Once you stop, the result is written into the page address. Use the share button or copy the address to send the total time and all laps as a link – whoever opens it sees exactly these times with the lap table and can then start timing themselves. Nothing is sent to us: the times live in the link itself.
Frequently asked questions
Does the stopwatch keep running if I close the tab?
Yes, if your browser allows local storage. When you reopen the page, it shows the time elapsed since start. In private mode the state is lost when the window closes.
Does the stopwatch show milliseconds?
The display shows hundredths of a second; internally the time is calculated to the millisecond. More digits would not add real precision, because reaction time when clicking is typically 0.1 to 0.3 seconds.
What is the difference between lap time and total time?
Lap time measures only the segment since the last lap click, for example one length in a pool. Total time keeps running since the start.
What is the difference between a stopwatch and a timer?
A stopwatch counts up with no limit to measure how much time has passed, for example during training. A timer counts down from a set time and sounds an alert once it reaches zero.
Can I use the keyboard?
Yes: Space starts and stops, L or Enter records a lap, R resets the stopped watch.
Is it accurate enough for races or official competitions?
It works well for training and personal timing. For official competition results it is not suitable, since reaction time when clicking or tapping (0.1 to 0.3 seconds) limits the accuracy of any hand-timed browser stopwatch.
Can I embed the stopwatch on my website?
Yes, it is available as an embeddable widget. As here, no account or install is needed; time and laps stay saved locally in the browser.
Sources and legal basis
- W3C: High Resolution Time (timing in the browser)
- MDN: Page Visibility API (behavior in background tabs)
As of: · Editorial policy
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