Online Stopwatch
How to use the stopwatch
The stopwatch starts counting the moment the page loads, so if you arrived here mid-experiment the clock is already running. Press stop to freeze it, resume to carry on from the same total, and reset to clear both the reading and the lap list.
Every control has a key, which matters when your hands are busy with whatever you are actually timing. The shortcuts work anywhere on the page, including in fullscreen.
| Key | Action |
|---|---|
| Space | Start or stop the stopwatch |
| L | Record a lap |
| R | Reset to zero and clear laps |
| F | Toggle fullscreen |
Stopwatch or timer: which one do you need
A stopwatch counts up from zero and keeps going until you stop it. You use one when the duration is the thing you are trying to find out: how long a lap took, how long the meeting actually ran, how long you can hold a plank.
A countdown timer works the other way. You give it a duration up front and it counts down to an alarm, which is what you want when the length is already decided and you would rather not watch the clock. Boiling an egg, a 25 minute work block, a two minute toothbrushing session.
A good share of people searching for a stopwatch actually want the second thing. If that is you, the countdown timer does the counting down, with presets for the common lengths.
Lap times and split times explained
Most stopwatch sites show one number per lap and leave you to guess which one it is. They are two different measurements and the table above shows both.
A lap time is the time since the previous lap. It answers "how long did that one take", so it is what you compare between repetitions: the fourth 400m repeat against the first, one batch of a task against the next.
A split time is the total elapsed at the moment you took the lap. It answers "how far into the whole thing am I", which is the number that matters when you are pacing against a target for the full distance.
Take four laps in a five kilometre run and the lap column tells you which kilometre you slowed on, while the split column tells you whether you are still on for the finish time you wanted. pomofox also marks the fastest and slowest lap once you have taken more than one.
Will the stopwatch keep running if I close the tab?
Closing the tab ends it. Nothing survives that, because the stopwatch runs entirely in the page and there is no server keeping count for you.
Switching to another tab, minimising the window or locking the screen is a different question, and the honest answer there is yes. Browsers throttle background tabs hard, so a stopwatch written the naive way, adding ten milliseconds to a counter on every tick, quietly loses minutes while you are away and comes back reading far too low.
This one stores the clock time at which you pressed start and works out the difference against the current clock time on every repaint. The browser can throttle the repaints as much as it likes; the arithmetic still uses real elapsed time. Leave this page for an hour and the first frame you see on your return is already correct.
Frequently asked questions
Does the stopwatch keep time if my computer sleeps?
Yes. The stopwatch records the wall-clock instant you pressed start and subtracts it from the current time on every repaint, so it is not counting ticks that a sleeping machine would never fire. Shut the lid for ten minutes, open it again, and the reading jumps straight to the correct total rather than resuming from where it froze.
Can I export or copy my lap times?
Laps stay on screen as a plain HTML table for the whole session, so you can select the rows and copy them straight into a spreadsheet or a message. Nothing is uploaded and nothing is stored on a server. Pressing reset, or closing the tab, clears them for good.
Is there a fullscreen mode for a classroom or gym?
Press F, or use the full screen button, and the readout scales to the width of the display. It stays legible from the back of a classroom or across a gym floor, and the keyboard shortcuts keep working while you are in fullscreen.
Does it work without an internet connection?
After the first visit the page is cached by your browser, so it opens and runs with the network off. The stopwatch itself never needs a connection, because all the timing happens in your browser rather than on a server.
Related tools
- countdown timer for when you know the length in advance and want an alarm.
- flip clock for a full-screen clock on a spare monitor.
- pomodoro timer for focus sessions with pixel-art characters and breaks built in.