How to use the online stopwatch
- 1.
Start
Click “Start” or press Space. Time is shown to a hundredth of a second.
- 2.
Record laps
Click “Lap” (key L) while running. The table shows each lap, the difference from the previous lap and the total time.
- 3.
Stop and export
Stop with Space and export laps to CSV. “Reset” (key R) clears everything.
Accuracy and background running
The stopwatch uses the browser’s high-resolution clock (performance.now()) instead of counting timer ticks, so the result stays correct when the tab is inactive or the computer is busy. The display refreshes with your screen, typically 60 times a second.
The running state is saved locally in your browser. If you reload the page or close the tab mid-measurement, the stopwatch resumes with the correct time, counted from the original start. Nothing is sent to any server.
Laps: split, delta and total
Each lap has three values: the lap time (since the previous press), the delta against the previous lap (a minus sign means faster) and the total time since the start. The fastest and slowest laps are highlighted.
Example: laps of 10.00 s, 15.00 s and 8.00 s give totals of 10.00 s, 25.00 s and 33.00 s, and deltas of +5.00 s and −7.00 s. The CSV export uses a semicolon separator with a UTF-8 BOM; in spreadsheet apps set to a comma separator, choose “semicolon” when importing.
Using it for running, practice and work
Manual timing is limited by reaction time - usually 0.15-0.3 s at the start and again at the stop - so treat hundredths as indicative. The errors partly cancel out when the same person reacts to the same kind of signal.
| Use | How to use laps |
|---|---|
| 400 m track | Press L at each finish line; four laps of 1:30 make 1600 m in 6:00 - roughly a six-minute mile |
| Bike or rowing intervals | Lap at the end of each interval - the delta shows whether you are fading |
| Speech rehearsal | Lap after each slide or section |
| Practice exam | Lap after each question, then export to CSV |
To convert the display to seconds, multiply minutes by 60: 02:05.40 is 125.4 s.
Keyboard shortcuts and fullscreen
| Key | Action |
|---|---|
| Space | start / stop |
| L | lap |
| R | reset |
Shortcuts are ignored while the cursor is in a text field. The fullscreen button enlarges the digits - handy in a classroom, at the gym or on a projector.
Frequently asked questions
How accurate is it?
+
It uses the browser’s high-resolution clock, so the stopwatch itself is accurate well below a hundredth of a second; human reaction time when clicking is the main source of error.
Does it keep running in another tab?
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Yes. Elapsed time is computed from a clock, not from a refresh counter, so you see the correct time when you come back.
Will the time survive a page reload?
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Yes, as long as your browser allows local storage. A running stopwatch resumes with the correct time and your laps are kept.
How do I export lap times?
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Click “Export CSV”. The file lists the lap number, lap time, delta and total time and opens in Excel, LibreOffice or Google Sheets.
What are the keyboard shortcuts?
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Space - start/stop, L - lap, R - reset.
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