Stopwatch
Simple stopwatch with lap timing.
How to use
- Press Start to begin timing or hit the spacebar for hands-free control.
- Tap Lap to record a split without stopping the running clock.
- Use Pause to freeze the display, then Start again to resume from the same moment.
- Press Reset to clear the current time and lap history when you are done.
- Copy or export your laps if you need to share or save them.
Frequently asked questions
How accurate is this stopwatch?
It uses performance.now() under the hood and is accurate to the millisecond. Tiny drift can occur on background tabs because browsers throttle inactive timers, so keep the tab active for the most precise reading.
Do my lap times survive a page refresh?
No. The stopwatch runs entirely in your browser memory, so refreshing the page clears all timing data. Copy or export your laps before you leave the page if you need to keep them.
Can I use keyboard shortcuts?
Yes. Spacebar starts and pauses, L records a lap, and R resets. This makes it easy to time things hands-free during a workout or experiment.
Does the stopwatch keep running with the tab in the background?
The timer continues, but browser tabs that lose focus are throttled by the OS, so the visible display may update less often. The elapsed time is recalculated correctly when you come back to the tab.
Lap vs split: two readings of the same clock
A running stopwatch offers two views of elapsed time. Split (cumulative) time is total time since start at each press: 2:00, 4:10, 6:25. Lap time is the interval since the previous press: 2:00, 2:10, 2:15. Splits answer "am I on pace overall?"; laps answer "which segment was slow?" Runners pacing a 5 km race watch splits against target; a coach diagnosing where the race fell apart reads laps. Recording both, as this stopwatch does, costs nothing and preserves both analyses.
Timing accuracy in a browser, honestly stated
Browser timers are accurate to a few milliseconds under normal conditions, and the displayed centiseconds are real. Two caveats apply to any software stopwatch: human reaction time adds roughly 150-250 ms at each press, which dwarfs the device's error in hand-timed events; and background tabs may be throttled by the browser, so keep the stopwatch visible during long sessions. For science-fair rigour, what matters is consistency... the same person pressing under the same conditions... more than absolute precision.
Uses beyond the gym
- Interval training: time work and recovery segments precisely instead of guessing.
- Process auditing: timing how long routine tasks genuinely take (the results consistently surprise) turns time-management theory into data.
- Cooking and lab work: laps mark each stage's duration in multi-step procedures.
- Presentations: rehearse against the clock; discovering the 10-minute talk runs 14 is cheaper in rehearsal.
- Children's games and chores: racing the stopwatch remains undefeated motivation technology.
Getting clean numbers from hand timing
- Decide the start and stop events precisely before timing ("when the foot crosses the line", not "around the finish"). Most hand-timing noise is definitional, not mechanical.
- Same timer, same person, same vantage point across trials... consistency converts reaction-time error from noise into a constant that cancels out in comparisons.
- For short events under 10 seconds, time several repetitions and divide: ten pendulum swings timed once beats one swing timed ten times.
- Record laps immediately; memory reorders numbers within minutes.
- Report hand-timed results to tenths. The display shows hundredths; your thumb does not.
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