Start, stop, and lap with a high-precision browser stopwatch. Records lap times automatically.
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A stopwatch counts up from zero, used to measure elapsed time. A timer counts down from a set duration. Stopwatches are used in sport, science experiments, and productivity (measuring how long tasks actually take, vs how long you thought they would).
In track athletics, a lap time is the time for each individual lap, while the split time is cumulative from the start. Coaches use lap times to identify where a runner gains or loses pace during a race. The last 400m of a 10,000m race often shows significant variation.
Accurately measuring how long tasks take (time tracking) is one of the most powerful productivity tools. Most people underestimate task duration by 25–50% (the planning fallacy). Tracking real time over a week calibrates your estimates dramatically.
Digital stopwatches are accurate to 1/100th of a second. Mechanical stopwatches, once the gold standard, are accurate to around ±0.1s per minute. For Olympic timing, photoelectric sensors combined with digital clocks measure to 1/1000th of a second.
JavaScript's Date.now() is accurate to about 1 millisecond in most browsers. However, Firefox and Chrome deliberately reduce timer precision to prevent timing attacks. For scientific measurements, use dedicated hardware.
High-intensity interval training often uses fixed work/rest intervals. Use the lap button to mark the start of each interval so you can then review the lap times to confirm you kept consistent intervals, even when exhausted.
A high-precision browser stopwatch with lap timing. Click Start to begin, Lap to record split times, and Stop then Reset to control the timer.
Timing a presentation
Start when you begin speaking; stop when you finish — aim for under 10 minutes
Interval training: 30 seconds on, 30 seconds rest
Use the lap button at each interval boundary to track each set
Cooking: timing pasta to al dente
Start when the pasta goes in; check at each minute mark using laps
The first mechanical stopwatch was invented in 1776 by Jean-Moïse Pouzait, a Genevan watchmaker. Sports timing was standardised in the late 19th century. Digital stopwatches accurate to 0.01 seconds were introduced at the 1972 Munich Olympics, replacing the human-read mechanical timers that had been used for decades.
It is useful for everyday timing, practice intervals, cooking, meetings, and rough experiments, but it is not a certified timing instrument. Browser rendering and device scheduling can delay the visual display even when elapsed time is calculated correctly. Use dedicated timing equipment for races, laboratory work, billing, or any result with legal or financial consequences.
Yes. Pause when you need to stop measuring, then resume to continue the same elapsed interval. A reset starts a new measurement, so record or copy any result you need before clearing it. For repeated training intervals, write down each lap or use a purpose-built sports timer that preserves a complete history.
A background tab may be throttled by the browser, especially on a phone or when the device is conserving power. The display may stop refreshing and then catch up when you return. Keep the page active for the most reliable visual readout, and do not use it as an alarm or safety-critical timer.
Pause the timer before copying or writing down the displayed interval so the value does not change while you record it. Note whether the run includes setup time, pauses, or laps, and use the same convention for every trial. Repeat measurements when a rough browser timing is not enough for your comparison.