Online Stopwatch
Simple stopwatch with lap times.
A stopwatch for workouts, cooking, presentations and experiments — with lap splits for intervals.
How to use
- Click Start — the timer runs with 1/10-second precision.
- Hit Lap to record split times without stopping.
- Reset clears everything.
About this tool
It keeps running while the tab is open and uses your device clock for accuracy.
No data is recorded or uploaded anywhere.
How it works
A stopwatch measures elapsed time between a start event and a stop event. This tool reads the browser’s high-resolution timer (performance.now()), precise to fractions of a millisecond — far finer than the one-second ticks shown on screen.
Lap times stamp the elapsed time each time you press Lap without stopping the clock; split times show each lap’s individual duration (lap 3’s split = lap-3 stamp minus lap-2 stamp). Coaches live on splits: they reveal pacing changes you cannot feel in the moment.
What you see is not the full precision. The display refreshes about 60 times per second, so the last digit flickers — but the recorded final time uses the exact reading captured the instant you hit stop.
Worked examples
Track intervals: 400 m rep in 72.4 s, next in 71.8 s. The 0.6 s split difference proves the second rep was faster, even though both felt identical.
Cooking by feel: Pasta needs 9 minutes. Start the stopwatch when it hits the water, tap Lap at minute 6 when the sauce ingredients go in — no mental math.
Quick reference
| Benchmark | Time |
|---|---|
| Human blink | ~0.1–0.15 s |
| Typical reaction time | ~0.25 s |
| 100 m world record | 9.58 s |
| Marathon world record | ~2:00:35 |
| 1 min 30 s in decimal | 1.5 min = 90 s |
Frequently asked questions
How precise is it?
Display updates every 50ms; device-clock based, accurate to about a tenth of a second.
Does it run in the background?
It keeps counting while the tab is open; closing the tab stops it.
Is anything tracked?
No — nothing leaves your browser.
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