UsefulTab
Stopwatch
A precise stopwatch with lap times, running in your browser.
Time anything precisely, locally
A stopwatch measures how long something takes. Press Start to begin, Stop to pause, and Start again to resume from where you left off; Reset returns it to zero. The Lap button records a split — the total elapsed time at that moment and the gap since the previous lap — so you can time repeated intervals like laps of a track or steps of a task. Each lap is listed with its number, split, and total. Elapsed time is measured against the browser's high-resolution performance clock rather than by counting ticks, so the reading stays accurate and does not drift even if the tab is throttled. Everything runs in your browser — nothing is ever uploaded.
Common questions
How accurate is the stopwatch?
The display updates about 60 times a second and shows hundredths of a second. The underlying measurement uses the browser's high-resolution performance clock and is computed as (now − start), so it reflects real elapsed time precisely rather than accumulating error from a counter.
What does the Lap button do?
It records a split at the moment you press it: the total elapsed time so far, and the time since your previous lap. Use it to time repeated intervals — like laps of a run or stages of a process — without stopping the clock. Laps are numbered and listed newest last.
Does it keep timing if the tab is in the background?
The elapsed time stays accurate because it is measured against the device clock, not by counting ticks — so when you return to the tab the reading is correct. The visual updates may pause while the tab is backgrounded and throttled by the browser, but the time itself does not drift.
Can I resume after stopping?
Yes. Stop pauses the clock and keeps the elapsed time; pressing Start again resumes from that point. Reset is what clears the elapsed time and all recorded laps back to zero.
Is any data uploaded?
No. The stopwatch runs entirely in your browser with JavaScript. Your times and laps stay on your device and are never sent to a server — it is fully client-side and private.