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⏱Online stopwatch

✓ Tested & verified Updated: How this works

Stopwatch

0:00.00

  • Laps0
  • Fastest lap—
  • Average lap—

    Space starts and stops · L takes a lap · R resets

    One thing a month worth timing

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    One thing a month worth measuring or capping with a clock — a payroll trap, a nap length, a meeting that never gets added up. Two sentences and the tool.

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    How accurate is a browser stopwatch?

    The TimerPlan stopwatch is accurate to the hundredth of a second and stays accurate in a background tab, because it stores the clock time you started at and subtracts rather than counting frames. A stopwatch built the usual way — adding a hundredth on every animation frame — stops receiving frames the moment the tab loses focus, so it quietly runs slow by exactly as long as you were away.

    What no browser can promise is your reaction time on the button. Human reaction to a visual cue is around 200 to 250 milliseconds, which dwarfs anything the page contributes, so treat readings as good to about a quarter of a second when a hand starts and stops them.

    Laps keep both numbers that matter: the split for that lap alone and the total since the start, with the fastest and the average across all of them.

    Three keys run the whole page, which is the point — a stopwatch you have to aim a mouse at is a stopwatch that is late twice per lap.

    KeyDoes
    SpaceStart and stop
    LTake a lap
    RReset everything

    Laps are listed newest first, each with its own split and the running total, so the number you want is at the top rather than at the end of a growing list.

    For counting down rather than up, the online timer is the other direction, and the count-up timer sits between the two — it counts up but towards a target, which is what you want for an hour of practice rather than a set of repeats. For tempo rather than duration, the metronome holds a beat and the BPM counter reads one back. To turn a set of elapsed times into hours for an invoice, the hours calculator does the arithmetic properly, in both h:mm and decimal.

    Frequently asked questions

    What is the difference between a lap and a split?

    A split is the time for one lap on its own; the total is the time since the start. Runners usually want splits — lap four was 1:52 — while race organisers want totals, because that is what goes on the result. Most online stopwatches show one and make you subtract for the other; both are recorded here for every lap, along with the fastest and the average across them.

    Does it keep timing if I switch tabs or minimise the window?

    Yes, and this is the difference that matters. The elapsed time is the gap between the clock time you started at and the clock time now, so a browser that stops drawing the page while it is hidden costs nothing at all — the number is correct the instant it becomes visible again. There is nothing accumulating that could fall behind.

    Can I use it for interval training?

    You can, though a countdown fits work-and-rest better: the stopwatch tells you what happened, a timer tells you when to stop. The usual arrangement is the interval plan under time plans for the structure and this page for the actual splits, since knowing lap eight was four seconds slower than lap two is the part a countdown cannot give you.

    Why does it show hundredths rather than milliseconds?

    Because milliseconds would be false precision on a hand-operated timer. The page can measure to about a millisecond, but the button is pressed by a person, and the variation in a human press is a hundred times that. Sports timing bodies use hundredths for hand timing and reserve thousandths for electronic starts and finishes, which is the same reasoning.

    How this works

    Starting records the current clock time; the display is that value subtracted from the current time, plus whatever was accumulated by previous runs, which means no frame ever adds to a total and a tab that stops being drawn cannot fall behind. Stopping adds the current run to the accumulated total and leaves the clock reference alone. A lap records the elapsed time at that instant and the difference from the previous lap; the fastest is the smallest of those differences and the average is their mean, both recomputed on every lap rather than kept as running totals. The display shows hundredths because that is the resolution a hand-operated stopwatch can honestly claim — the page itself resolves to about a millisecond, but a human press varies by a hundred times that. A screen wake lock is held while the stopwatch runs. Nothing is stored and nothing is uploaded; laps live in the page until you reset or leave.

    Sources:

    What to read from the numbers

    The average lap is the honest one. A single fast lap is noise; the average across six is a measurement.

    Fade shows up in the spread. When the gap between fastest and average grows across a session, that is fatigue, and it is visible here without any calculation.

    Reaction time is a floor. Anything under about a quarter of a second between two hand presses is inside the noise of the hand, not the stopwatch.