Online Stopwatch
Press start and it counts up in hundredths. L records a lap without stopping the clock, so you can time each length, each rep or each attempt and compare them afterwards.
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About the stopwatch
A stopwatch answers a different question from a timer. A timer knows how long something should take and tells you when it is up; a stopwatch does not know, and the whole point is to find out. That is why it counts up and why it has laps.
The lap button is the part worth understanding. Pressing it records the time at that instant and starts measuring the next segment, without ever stopping the overall clock. So you get both numbers: how long each individual lap took, and how far into the session each one finished. Runners want the first, anyone timing a process wants the second, and the list here shows both side by side.
Hundredths are displayed because that is what people expect from a stopwatch, but they should be read with some scepticism. Your reaction time on the start and stop is somewhere between a tenth and a quarter of a second, which is ten to twenty-five times larger than the last digit. For anything where hundredths genuinely decide the result, the timing has to be triggered by the event rather than by a thumb.
What it is reliably good for is comparing things of your own: this attempt against that one, this lap against the last, this batch against the one before. The reaction time error is roughly the same on every press, so it mostly cancels out of the comparison even though it is present in each absolute figure.
What people use it for
- Timing laps, lengths and intervals in training
- Finding out how long a task actually takes before scheduling it
- Timing a speech or presentation in rehearsal
- Cooking steps where the total matters more than any one stage
- Comparing two ways of doing the same job
How it works
The elapsed time is the difference between now and the moment you pressed start, read fresh from the clock each repaint. Pausing banks what has run so far and starting again adds to it, so a stopwatch you stop and start ten times is still exact.
It repaints about twenty-four times a second, which is what makes the hundredths move smoothly. A hidden tab repaints far less often, but since the number is worked out from the clock rather than accumulated, the display is correct the instant you come back to it.
Laps are held in the page only. Reloading clears them, and nothing about a session is stored or sent anywhere.
- Space
- Start or pause.
- R
- Reset.
- L
- Record a lap.
- Tab title
- Shows the time left, so a background tab still tells you.
Questions
What is the difference between a lap and a split?
A lap is the time for one segment on its own. A split is the total elapsed time at the moment that segment ended. Both are shown for each press, so you do not have to pick in advance.
Does the lap button stop the clock?
No. It records the moment and starts the next lap while the overall time keeps running. Only pause stops the clock.
How accurate is it?
The measurement itself is accurate to the millisecond, because it is a difference between two clock readings. Your own reaction time on the start and stop is the limiting factor, and that is typically a tenth to a quarter of a second in each direction.
Does it keep counting if I switch tabs?
Yes, and it stays exact. The elapsed time is worked out from the clock rather than by counting ticks, so a throttled background tab changes how smoothly the digits move and nothing else.
Can I keep my lap times?
Only while the page is open. They are not stored anywhere, so copy them out before reloading if you need them.
Is there a keyboard shortcut?
Space starts and pauses, L records a lap, and R resets. They work anywhere on the page except while you are typing in a field.
Why does the last digit jump rather than counting every hundredth?
It repaints around twenty-four times a second, so it skips values. Painting every single hundredth would cost battery and you could not read them anyway — the recorded lap times are exact regardless of what the display had time to show.
I need to count down instead.
Use the countdown on the timers page, or one of the fixed lengths listed there. The stopwatch only counts up.