Stopwatch
This online stopwatch times to the hundredth of a second and records laps without stopping. Press Start to begin, Lap to save a split, and Stop to pause. Each lap shows its own time and the running total, so you can compare intervals during sports, workouts, experiments or any task you want to time.
How to use the Stopwatch
- Press Start to begin timing; the display shows minutes, seconds and hundredths.
- Press Lap to record a split while the stopwatch keeps running.
- Press Stop to pause, and Start again to continue from the same time.
- Press Reset to clear the time and all laps.
Formula
lap time = total at this lap - total at previous lapTime is measured with performance.now(), the browser's high-resolution monotonic clock, so it is not affected by changes to the system clock. The display rounds to hundredths of a second.
Common uses
- Running and swimming laps
- Interval and circuit training
- Timing cooking steps
- Science experiments and reaction times
- Measuring how long tasks really take
Accuracy
The clock itself is precise to well under a millisecond, but a hand-started stopwatch includes human reaction time of roughly 0.15 to 0.3 seconds. For official races, use electronic timing; for training, consistent hand timing is perfectly useful.
Stopwatch questions
How accurate is this online stopwatch?
It reads the browser's high-resolution clock and displays hundredths of a second, which is as precise as any handheld stopwatch. The limiting factor is human reaction time when pressing Start and Stop, typically 0.15 to 0.3 seconds, so use electronic timing for official competition.
What is the difference between a lap and a split?
A lap time is how long one segment took, while a split is the total elapsed time at that point. This stopwatch shows both for every lap: the lap time and the running total. Coaches use laps to check pacing and splits to track race progress.
How do I use lap timing for interval training?
Press Lap at the end of each work interval and each rest interval, so every effort and recovery gets its own time. Comparing lap times shows whether your pacing stays even. Aim for consistent efforts before trying to make them faster.
Will the stopwatch keep running if I switch tabs?
Yes. Time is calculated from the clock rather than counted tick by tick, so the elapsed time stays correct even if the browser slows down a background tab. The display catches up as soon as you return. Closing or reloading the tab resets the stopwatch.
How do I calculate pace from my stopwatch time?
Divide the time by the distance. A 5 km run in 25:00 is a pace of 5:00 per kilometer, or 12 km/h. For swimming, divide by the number of 100 m lengths. Use the speed converter to switch between km/h, mph and m/s.
Which sports benefit most from stopwatch timing?
Running, swimming, cycling time trials and rowing all rely on lap and split times. Stopwatches are also useful for HIIT and circuit training, rest periods between sets and rehabilitation exercises, anywhere precise, repeatable timing helps track progress. Recording laps over several sessions also shows long-term progress.