Online Stopwatch
Stopwatch with laps, splits, fastest lap and CSV export. Runs in your browser.
About this online stopwatch
This online stopwatch measures elapsed time to the hundredth of a second and records laps with splits. It's for runners and coaches, students timing experiments, teachers timing speeches, and anyone who needs to know exactly how long something took.
Press Start or the Space bar, press L at each lap, and read the lap time, the running total and how much faster or slower each lap was than the one before. With three or more laps, the fastest and slowest are marked, and the average is shown.
The time comes from timestamps, so it stays exact when you switch tabs, lock your screen or reload the page. When you're done, copy the laps straight into a spreadsheet or download them as a CSV file.
Features
Laps and splits
Each row shows the lap number, lap time, split (total so far) and the difference from the previous lap, green when faster and red when slower.
Fastest, slowest, average
Summary tiles show the lap count, average lap, and the fastest and slowest lap with their numbers.
Copy or CSV
Copy laps puts a tab-separated table on your clipboard that pastes into columns. Download CSV saves the same table as a file.
Keeps going after a reload
The start time and laps are saved in this browser, so an accidental refresh doesn't wipe a 40 minute session.
Keyboard first
Space starts and pauses, L records a lap, R resets and F goes full screen. Typing in a box never triggers them.
Interval beep
Optional beep every 10 seconds, 30 seconds, minute or 5 minutes, with your choice of sound and volume. The beeps are scheduled on the audio clock, so they stay on the beat.
Full screen and screen on
Huge digits for a gym or classroom, and Keep screen on stops the display dimming while the watch runs.
How to use the online stopwatch
- 1Press Start or the Space bar to begin timing.
- 2Press Lap (or L) at each lap. The table shows lap time, split and the difference.
- 3Pause, then copy the laps or download them as a CSV file.
When to use it
Track and pool laps
Press L as each lap ends and watch the differences. If a 400 m lap drops from 1:32 to 1:38, you see +0:06.00 in red at once. To turn times into pace per km or mile, try the pace calculator.
Science practicals
Time each swing of a pendulum or each trial of a reaction, then paste the laps into your spreadsheet for averages and graphs.
Speeches and presentations
Run it full screen while you rehearse and mark a lap at each section, so you know which part runs long.
Tasks and billing
Time a phone call or a job. Pause when you're interrupted and resume later; paused time isn't counted.
Drills and planks
Turn on a beep every 30 seconds and switch exercises on each beep without looking at the screen.
What is the difference between a lap time and a split time?
A lap time is how long one segment took. A split time is the total time from the start to the end of that segment. Say you run three laps that end at 1:30, 3:05 and 4:35 on the clock. Those are the splits. The lap times are 1:30, 1:35 and 1:30.
Coaches care about both. Splits tell you whether you're on target for the finish. Lap times tell you whether your pacing is even. This stopwatch shows both in every row, plus the change from the lap before.
How accurate is an online stopwatch?
The clock itself is very accurate. The stopwatch records the moment you press Start and the moment of each lap using your device's clock, which reads to the millisecond. It doesn't add up ticks, so a slow or busy tab can't make it drift. Leave it for an hour in a background tab and the elapsed time is still exact when you come back.
The real limit is you. Human reaction time to something you see is roughly a quarter of a second, and it varies from press to press. Hundredths are useful for comparing laps you timed the same way, but for official race timing you need electronic gates. A display that refreshes 60 times a second also means the last digit you see is never more than about 17 milliseconds old.
Does the stopwatch keep running if I close or reload the page?
If you reload, yes. The start time, any paused time and your laps are kept in your browser's local storage, so the watch picks up exactly where it was. If you close the tab and open the page later, it carries on too, counting all the time in between.
Nothing is uploaded, and nothing syncs between devices. Clearing your browser data, or using a private window, removes the saved session. Download the CSV if the laps matter.
Why use Mavros
| Mavros | Typical upload sites | |
|---|---|---|
| Laps after a reload | Kept in your browser | Lost on refresh |
| Lap comparison | Diff vs previous, fastest and slowest marked | Plain list of times |
| Export | Copy as columns or CSV | Often none |
| Background tab accuracy | Timestamp based, no drift | Some count ticks and drift |
| Interval beep | Every 10 s to 5 min, volume control | Rare |
| Ads and sign-up | None | Ads, sometimes a paid tier |
Tips
- Use the keyboard for laps. Pressing L is faster and more consistent than moving a mouse to a button.
- Turn off hundredths if they're distracting on a projector. Laps and exports still keep the full detail.
- Copy laps and paste into a spreadsheet cell: the lap, lap time, split and difference land in separate columns.
- To count down instead of up, switch to the online timer, which has an alarm and presets.
- For focused work sessions with breaks built in, the Pomodoro timer handles the switching for you.
Questions
How do I record a lap?
Press the Lap button or the L key while the stopwatch runs. The new row shows the lap time, the split and the difference from the previous lap.
What is a split time?
A split is the total time from the start up to a lap press. A lap time is just that one segment. The table shows both side by side.
Is this stopwatch accurate to a hundredth of a second?
Yes, the clock is read to the millisecond and shown to hundredths. Your reaction time when pressing the button, roughly a quarter of a second, matters far more than the clock.
Does it keep time in a background tab?
Yes. Elapsed time comes from timestamps, not counted ticks, so throttled background tabs don't slow it. The tab title shows the elapsed time when the browser updates it.
Can I export my laps?
Yes. Copy laps puts a tab-separated table on your clipboard for spreadsheets, and Download CSV saves it as a file. Both include every lap, even beyond the 500 shown on screen.
What do the keyboard shortcuts do?
Space starts and pauses, L adds a lap, R resets and F toggles full screen. They're ignored while you type in a field, so they never get in your way.
Can it beep at set intervals?
Yes. Choose a beep every 10 seconds, 30 seconds, minute or 5 minutes, then pick a sound and volume. Beeps follow elapsed time, so pausing pauses them too.
Are my times stored anywhere?
Only in this browser's local storage, so a reload doesn't lose them. Nothing is sent to a server. Reset clears the session.