How to use this stopwatch
- Start with the green button or the Space bar. On a phone the buttons are thumb-sized for timing trackside.
- Lap each time the runner, swimmer or machine cycle passes your mark. The current lap counts up under the main readout.
- Stop to pause; Resume carries on from the same time. Reset only works when stopped, so a stray tap can't wipe a run.
- Export CSV for a spreadsheet, or Save to history to keep the session in this browser.
Keyboard shortcuts
| Space or Enter | Start / stop |
| L | Record a lap |
| R | Reset (while stopped) |
| F | Full screen, for projecting on a wall or a gym TV |
Laps, splits and what the numbers tell you
A lap is the time between two presses; a split is the running total at that press. Coaches read both: splits show whether a runner is on schedule for a target, laps show whether the effort is even. The table marks each lap faster (green) or slower (amber) than the previous one and than your average.
The consistency figure is the coefficient of variation: the standard deviation of your laps as a percentage of the average lap. Under about 2% on hand-timed track laps is very even pacing; allow for the fact that each press carries human reaction delay. The 2nd half vs 1st figure compares the average lap of the second half with the first. A minus sign means a negative split, i.e. you finished faster than you started.
Want a written read-out? Once you have two or more laps, the pacing analysis can describe the pattern, flag odd laps and suggest a target for next time.
Splitting one long effort into laps is how you find the exact stretch where things changed. A leaf’s day has its own split times: light reactions run only while the sun is up, and ahaboo narrates how the rest of photosynthesis fits around them.
Why it stays accurate in a background tab
Browsers slow down timers in hidden tabs, so a stopwatch that adds up 10 ms "ticks" drifts badly the moment you switch apps. This one never counts ticks. It stores the moment you pressed Start (from performance.now(), the browser's monotonic clock) and computes elapsed time as now minus start whenever the screen redraws. Hide the tab, lock the phone, even reload the page: the start time is saved, so the reading is still right when you come back.
The 0.001 s display is honest about the arithmetic, not about you. Screens redraw 60–120 times a second, and a human thumb adds roughly 0.15–0.25 s of delay at each press. Our accuracy guide works through where the real error comes from.
More timing tools
- Millisecond stopwatch: the same watch showing thousandths (00:00.000) by default.
- Lap timer: lap timing tips for track, pool, karting and time studies.
- Multiple stopwatches: time up to 12 athletes, lanes or machines side by side.
- Split timer: race against a target pace and see ahead/behind on every split.
- Pace and lap time calculator: turn a goal time into a lap-by-lap plan.
- Reaction time test: measure the delay your thumb adds to every press.
Questions people ask
Is this online stopwatch free and does it need an account?
It is free, with no signup and no install. Laps and saved sessions are stored only in your own browser (localStorage), and you can clear them any time from the history panel or the privacy page.
Will the stopwatch keep running if I switch tabs or lock my phone?
Yes. Elapsed time is calculated from the saved start timestamp rather than by counting timer ticks, so throttled background tabs, a locked screen or even a page reload do not change the reading.
How accurate is it?
The browser clock is accurate to well under a millisecond, and the display can show thousandths. The real limit is the person pressing the button: human reaction adds roughly 0.15–0.25 s, which is why official athletics uses electronic timing for records.
What is the difference between a lap and a split?
A lap time is the time for one segment, from one press to the next. A split is the cumulative time from the start to that press. This stopwatch records both for every lap.
How many laps can I record?
There is no practical limit. Thousands of laps fit in browser storage, and the CSV export includes every lap and split in both formatted time and milliseconds.
Is an online stopwatch better than the one on my phone?
For desk and coaching work it is often easier: a big readout you can put in full screen or on a projector, keyboard control, a lap table with stats, copy-to-clipboard and CSV export. For timing away from a computer, open this page on your phone; it works the same and needs no app.
Can I hear a sound when I start, stop or record a lap?
Yes. Turn on Sound under the readout for a short beep on start, stop and every lap. It is off by default.
Can I use it with the keyboard?
Yes: Space or Enter starts and stops, L records a lap, R resets while stopped and F toggles full screen. Shortcuts are ignored while you are typing in a text field.