Stopwatch
Track time with centisecond precision and record laps.
Laps
No laps yet. Press Lap while the timer is running.
What Is an Online Stopwatch?
A stopwatch measures elapsed time with a precision the wall clock cannot: start it, stop it, and read exactly how long something took — down to hundredths of a second. This one runs in your browser with Start, Lap, and Reset controls, big readable digits, and a lap list that records each split as you go. Timing a run, a presentation, a chess clock substitute, a science experiment, or how long the kettle actually takes — if it has a beginning and an end, a stopwatch is the honest referee.
The lap function is what separates a stopwatch from a mere timer display. Each lap press freezes a split time while the master clock keeps running, so you can measure segments within a whole: every length of a swim, every section of a speech, every round of a workout. Comparing laps is where insight lives — the runner whose laps slow steadily is pacing wrong; the speaker whose third section balloons knows exactly what to cut.
How to Use the Stopwatch
- Click "Start" to begin timing.
- Click "Lap" at each segment boundary to record a split — the total keeps counting.
- Click Stop (Start toggles) when finished and read the final time and the lap list.
- Click "Reset" to clear the clock and laps for the next timing.
Precision, Honestly Stated
The display resolves to centiseconds (hundredths of a second), and because the elapsed time is computed from the system clock rather than by counting screen refreshes, it stays accurate over long runs and survives tab-switching. The true limit is the human pressing the button: reaction time to a start or finish signal is roughly 0.1–0.25 seconds for everyone, which is why hand-timed results in sports are conventionally rounded and why photo finishes exist. For practice timing, cooking, talks, and experiments, a stopwatch's precision comfortably exceeds the precision of the thing being measured.
Practical Timing Ideas
- Rehearse talks with lap-per-section: the split list shows exactly which slide eats your slot.
- Time recurring tasks for a day — email, commute segments, meeting overruns; most people are surprised by at least one number, and that surprise is the productivity insight.
- Classroom and lab work: reaction-time demos, pendulum periods (time 10 swings and divide — the classic trick for beating reaction error), and any before/after comparison.
Does the stopwatch stay accurate if I leave the tab?
Yes. The stopwatch calculates elapsed time from your device's clock each time it reads it, rather than accumulating frame by frame, so background tabs, screen locks, and switching apps do not cause drift — when you return, the displayed time is the true elapsed time. Just remember it cannot survive closing the tab or the browser entirely.
What does the Lap button actually record?
Each press records a lap entry — the cumulative time at that moment and, by comparing consecutive laps, the duration of that segment. Athletes read laps as splits (how fast each portion was); speakers read them as section times. Recording laps never interrupts the main clock, which is the whole point: segments and total, measured simultaneously.
How precise is an online stopwatch versus a phone app or physical stopwatch?
The clock source is the same quartz-accurate system time in all three; differences are display refresh and button response, worth a few hundredths of a second at most. All are far more precise than the human operating them. For anything short of sanctioned competition — where electronic triggering replaces thumbs — this stopwatch measures as well as any device you own.
Stopwatch or countdown timer — which do I need?
If you know how long something should take and want to be told when time is up (cooking, intervals, focus sessions), that is a countdown timer — it runs down to zero and alerts. If you do not know how long something will take and want to find out (a run, a task, a rehearsal), that is the stopwatch. Timing a race to a target uses both: stopwatch for the measurement, the target in your head.