Answer: A precise online stopwatch with lap and split timing that keeps running accurately in your browser tab.
Millisecond-precision stopwatch with lap tracking.
This online stopwatch measures elapsed time with precision to hundredths of a second, using your device's internal clock. It works entirely in your browser, so nothing is uploaded, and it is handy for timing workouts, cooking, experiments, presentations, or any task where you need an accurate elapsed-time reading without installing an app.
A stopwatch counts up from zero, while a timer counts down from a set value. This page covers the stopwatch case: press start when the event begins, stop when it ends, and read the total elapsed time. Lap or split buttons, when available, record intermediate times without stopping the clock.
Modern browsers rely on high-resolution timestamps defined by the W3C High Resolution Time specification, which reports time with sub-millisecond precision. For user-facing timing the practical accuracy is limited by human reaction time — typically around 200 to 250 milliseconds between seeing an event and clicking — rather than by the clock itself.
Because timing runs on your device's own clock, no network connection is needed once the page is loaded, and timing does not drift if your internet slows down. For official or scientific measurement, calibrated dedicated equipment is still the standard, but for everyday timing a browser stopwatch is accurate far beyond what human reflexes can exploit.
Stopwatch numbers mean more with context. The men's 100 m world record of 9.58 seconds was set by Usain Bolt in Berlin in 2009, and his 200 m record of 19.19 seconds came at the same meet. Elite marathoners finish 42.195 km in about two hours; the fastest certified marathon ever run is 2:00:35 by Kelvin Kiptum in Chicago in 2023.
The table below lists several world-record times across running events. Timing rules matter in these records: World Athletics ratifies sprint records only when measured with fully automatic timing to hundredths of a second and backed by wind readings within +2.0 m/s.
| Event | Men's world record | Record holder | Year |
|---|---|---|---|
| 100 m | 9.58 s | Usain Bolt | 2009 |
| 200 m | 19.19 s | Usain Bolt | 2009 |
| 400 m | 43.03 s | Wayde van Niekerk | 2016 |
| 800 m | 1:40.91 | David Rudisha | 2012 |
| Marathon | 2:00:35 | Kelvin Kiptum | 2023 |
When timing repetitions — laps, sets, or segments — record a reading at each transition rather than trying to reconstruct splits afterward. Splits from memory are unreliable past two or three intervals, while a recorded sequence preserves both the individual times and the total.
For interval training, common work-to-rest structures include 30 seconds on / 30 off, 40/20, and 60/60. Timing these with a stopwatch is straightforward: start the clock at the beginning of the first work interval and note the elapsed reading at each switch, or use the countdown timer page for rest periods paired with this stopwatch for work periods.
Human reaction time is the dominant error source in any hand-timed measurement. Studies of simple reaction time typically report means around 200–250 milliseconds for a visual stimulus and a button press, and values grow with fatigue and surprise. So treat single hand-timed readings as accurate to within a quarter second, and average several trials when comparing close results — the average of repeated measurements is a far better estimate than any single click.
How accurate is this online stopwatch?
It uses your browser's high-resolution clock, which keeps time with sub-millisecond precision. In practice, accuracy is limited by human reaction time — roughly 0.2 to 0.25 seconds — so measured intervals are typically accurate to within a quarter second, far better than counting seconds aloud but not a substitute for certified timing equipment.
What is the difference between a stopwatch and a timer?
A stopwatch counts upward from zero to measure how long something takes. A timer counts downward from a value you set and alerts you when time runs out. Use a stopwatch to measure duration and a timer to enforce a limit.
Does the stopwatch work offline?
Yes. Once the page has loaded, all timing runs locally on your device using its internal clock, so connection speed does not affect the measurement.
Why do stopwatches show hundredths of a second?
Hundredths (two decimal places) match the precision World Athletics requires for fully automatic race timing. Finer readings exist — the underlying clock is more precise — but hundredths reflect the smallest unit that is meaningful when a human presses the buttons.
What is a lap or split time?
A lap time records an intermediate elapsed reading without stopping the clock, so you can time segments of a session — for example each 400 m repetition in a running set — while total time keeps accumulating. Splits also reveal pacing consistency: comparing your first and last interval of a set shows whether you started too fast, which is one of the most common timing mistakes in endurance training and one of the easiest to fix once the numbers are visible.
Can I use a stopwatch for cooking or studying?
Absolutely. In the kitchen, timing each stage of a recipe — searing, simmering, resting — beats guessing, because overcooking is usually a timing error rather than a temperature error. For studying, techniques like the Pomodoro method alternate focused 25-minute work blocks with 5-minute breaks; a stopwatch measures the work block while a countdown timer handles the break, and either page here covers the job.