Online stopwatch

Stopwatch: the complete guide to time measurement

A stopwatch measures the time elapsed since a start: how long for this 10K, this lap, this set, this experiment? Unlike a timer that counts down a fixed duration, the stopwatch counts up to the hundredth of a second. This one runs entirely in your browser, with no cumulative drift, unlimited laps, statistics and CSV export.

Running · Swimming · Weight training · Games · Science labs · Freelance billing · Cooking · Presentations

In running and sports: live pace

Mark a lap at each kilometer (press L, without taking your eyes off the track): lap time for pace, total for the race, best lap highlighted in green. Set a pace target (e.g. 300 s/km): laps turn green or red depending on whether you're holding the pace. In swimming, fullscreen mode is readable from the pool edge; in weight training, time your rest periods between sets (60-90 s for hypertrophy).

At school and in science: clean measurements

Physics labs (free fall, pendulum, oscillations), PE, athletics games: timestamped laps export to CSV for the report spreadsheet. The monotonic base ensures measurements are immune to clock changes on classroom PCs — a crucial detail when a lab lasts a full class hour.

At work: bill your time in real time

Freelancers and consultants: start a lap per task or client, export to CSV at the end of the day — an objective timesheet for billing by the quarter hour. The session history keeps track of the week, without tracking apps or subscriptions. Timed meetings are shorter: putting a visible stopwatch on the shared screen naturally disciplines speakers.

Laps, splits, average: reading the table

Each row gives the lap (segment pace) and the total (race time). The best lap (green) and worst (red) reveal consistency; the average shows the sustained pace. A growing gap between laps = fatigue or poor management: adjust the next start. The pace target colors each lap green (held) or red (missed) for instant feedback.

Why the browser beats the phone stopwatch

Giant screen readable from a distance (the coach sees from the sideline), keyboard (Space/L/R faster than sweaty touchscreen), direct CSV export to Excel, session history, resume after reload: on a coach's or teacher's desk, the browser wins. And nothing is sent online — your times stay on your machine.

Monotonic precision: why it matters

A classic stopwatch uses Date.now(), sensitive to system clock changes and NTP synchronization. Ours uses performance.now(), a monotonic clock that never goes backward and doesn't drift. Result: even if your PC adjusts its clock mid-timing, the measurement stays exact. This is the same API browsers use to measure page load performance.