Stopwatch — Free Online Tool on Toolpile
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About Stopwatch
A browser stopwatch is one of those tools where precision, pause behavior, and what happens when the tab is backgrounded matter more than the UI. Here's how this one handles each, and when a browser stopwatch isn't the right choice.
Browser stopwatches claim millisecond precision, and most deliver it down to ~4-16ms depending on the OS's clock resolution. This tool uses `performance.now()` under the hood, which reports elapsed time to sub-millisecond resolution on modern browsers, then rounds to 10ms for display. If you need timing tighter than that (physics lab data, audio-sample alignment), a browser stopwatch is the wrong tool — use a hardware timer or an audio-sample-based recording.
For the actual common cases — workouts, cooking, reading speed, study sessions, board-game turn timers — the 10ms display is far finer than human reaction time (~250ms). You will never notice the missing precision.
Lap times here are absolute timestamps, not deltas. A lap at 02:15.230 means the total elapsed at that moment; the delta to the previous lap shows in the secondary column. Both numbers are preserved so you can export either format.
This stopwatch measures elapsed time, not by counting ticks but by subtracting the start timestamp from the current one on every display frame. That means even if Chrome throttles the background tab to 1 tick per second (which all modern browsers do), the displayed time stays accurate when you return — because it re-reads the current clock at that moment. Stopwatches built on `setInterval` counting +1 per tick drift badly under backgrounding; this one doesn't.
Caveat: sleeping your laptop pauses the OS clock. When you wake up, the stopwatch shows accurate elapsed time INCLUDING the sleep. If you want pause-when-sleeping behavior, that's a different feature (and arguably the wrong default — most users want 'time since I pressed start' not 'active screen time').
Is it accurate if I leave the tab in the background?
Yes. Elapsed time is computed from wall-clock timestamps, not accumulated ticks, so background throttling doesn't cause drift. Foreground the tab and the display immediately shows the correct elapsed time.
What happens if I refresh the page?
Refresh clears the stopwatch — the start timestamp lives in memory only. If you need persistence across refresh or sessions, a habit-tracker or time-tracker tool is the right fit. Stopwatches are ephemeral by design.
Does it work offline?
Yes, once the page has loaded. The stopwatch logic runs entirely in-browser with no network calls. You can disconnect and it keeps running.
Why does my phone stopwatch run while the screen is off and this one doesn't?
Your phone's native stopwatch is a system-level service that keeps running in the background because it has OS privileges. A browser stopwatch runs inside a tab; mobile OSs aggressively suspend tabs to save battery. On iOS Safari, backgrounded tabs can be suspended after ~30 seconds — the stopwatch keeps accurate elapsed time but the DOM won't update until you return. For strict background timing on mobile, use the phone's native app.
Can I run multiple stopwatches at once?
Open multiple tabs, each with its own stopwatch instance. State is per-tab. If you need to compare two timings on the same screen, a lap-based approach within one stopwatch is usually simpler.
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