How to use the stopwatch
- Start begins timing. The display shows hours, minutes, seconds and hundredths of a second.
- Stop pauses the clock. Press Start again to carry on from the same time — useful when you only want to time the active part of something.
- Lap records the time without stopping. Each row shows the lap number, the lap time (since the previous lap) and the total time; the newest lap is at the top.
- Reset sets the clock back to zero and clears the laps. Stop the stopwatch first: Reset is disabled while it runs, so a stray tap can’t wipe a timing.
On a computer you can keep your hands on the keyboard: Space starts and stops, L takes a lap and R resets after you stop. While the stopwatch runs, the browser tab shows the elapsed time, so you can see it from another tab.
It keeps running — even after a reload
The stopwatch does not count ticks. When you press Start it notes the exact moment from your device clock, and the display always shows now minus start. That is why it stays accurate when a phone locks the screen or a browser slows down a background tab: the moment the page is visible again, the display jumps to the correct time. The start moment and your laps are saved in this browser, so if you close the tab or reload by accident, the stopwatch is still running when you come back. Nothing is sent to a server.
Lap time or split time?
Runners and swimmers use two related numbers. A split (or cumulative time) is the total time from the start to a checkpoint — the “Total time” column. A lap time is the time for that segment alone, from the previous checkpoint to this one. If you pass the 400 m mark at 1:45 and the 800 m mark at 3:35, your splits are 1:45 and 3:35 and your lap times are 1:45 and 1:50. Even lap times mean even pacing, which is usually the fastest way to race.
On a standard 400-meter track, one lap time tells you your pace:
| 400 m lap | Pace per km | Pace per mile | Speed (km/h) |
|---|---|---|---|
| 1:20 | 3:20 | 5:22 | 18.0 |
| 1:30 | 3:45 | 6:02 | 16.0 |
| 1:40 | 4:10 | 6:42 | 14.4 |
| 1:45 | 4:23 | 7:02 | 13.7 |
| 2:00 | 5:00 | 8:03 | 12.0 |
| 2:15 | 5:38 | 9:03 | 10.7 |
| 2:30 | 6:15 | 10:04 | 9.6 |
| 3:00 | 7:30 | 12:04 | 8.0 |
For any distance and time, the pace calculator does the conversion for you.
How precise is a hand-timed stopwatch?
The display resolves hundredths of a second and the underlying clock is far finer than that, so the limit is your finger. Human reaction time to a visual signal is typically around 0.2 seconds, and you react once when you start and once when you stop, so hand timing can be off by a tenth or two in either direction. That is why athletics records require fully automatic electronic timing. For everyday use — workouts, speeches, reading drills, puzzle-cube solves, experiments in class — the error is negligible, and timing several attempts the same way keeps comparisons fair.
Stopwatch ideas
- Interval training: take a lap at the end of every work and rest period to see whether you are slowing down.
- Presentations: rehearse with laps at each section to find where you overrun.
- Reading speed: time a passage, then divide the word count from the word counter by the minutes.
- Work tracking: stop the clock during breaks so the total is your active time; add up several sessions with the time calculator.
Need to count down instead? Use the online timer, which beeps when time is up.
Frequently asked questions
Does the stopwatch keep running if I switch tabs or lock my phone?
Yes. It measures from the moment you pressed Start using the device clock, so the elapsed time is always correct, even if the browser pauses the page in the background. Reloading or closing the tab doesn’t stop it either — the state is saved in this browser.
How do I record lap times?
Press Lap (or the L key) while the stopwatch is running. Each lap shows its own time and the total time so far, newest first. Laps are kept until you press Reset.
Is there a keyboard shortcut to start and stop?
Yes: Space starts and stops, L records a lap and R resets once the stopwatch is stopped. The shortcuts work whenever you are not typing in a box; if a button has focus, Space presses that button instead.
How accurate is it?
The clock itself is accurate to well under a hundredth of a second. The real limit is human reaction time, about 0.2 seconds at each press, which is why official races use electronic timing.
What is the longest time it can measure?
It keeps counting for as long as you like; the display shows hours up to 99 and continues beyond. Because it is based on the start time, even a stopwatch left running for days stays correct.
Last updated: October 14, 2026