Online Stopwatch

Start, lap, stop

Press start and the display counts up in hundredths of a second. Lap records the moment without interrupting anything, so you can take as many as you need while it runs. Stop banks the time rather than clearing it, which means pressing start again continues from where you left off instead of beginning a new attempt. Reset is the button that clears everything, and it is deliberately the one you have to mean.

On a desktop the space bar starts and stops, L takes a lap and R resets, which matters more here than on most tools: the whole point of a stopwatch is that the moment you press the button is the moment being recorded, and a key under your finger is faster and more repeatable than moving a mouse to a target.

Laps and splits, which are not the same thing

This trips people up constantly, and most online stopwatches make it worse by showing only one of the two. A lap is the time since the last lap you took. A split is the total elapsed time at the moment you took it. Run four laps of four hundred metres and the lap column tells you how fast each individual lap was, while the split column tells you your time at eight hundred, twelve hundred and sixteen hundred.

Both are on every row here, along with the lap number, so you never have to subtract one reading from another to get the one you wanted. Once there are at least two laps to compare, the fastest and slowest are marked, which is the comparison people are almost always reaching for and otherwise have to scan the column to find.

The list is newest first. On a long session the lap you just took is the one you want to see, and putting it at the top means it is not somewhere off the bottom of the screen by lap twenty.

How accurate this actually is

The honest answer is that the software is far more precise than the person operating it, and pretending otherwise would be the useful thing to leave out.

Timing is taken from your device's clock, which is accurate to the millisecond, and the display shows hundredths because that is the finest unit anyone can meaningfully read while it moves. Against that, human reaction time to a visual cue is roughly 200 to 250 milliseconds, and it applies twice: once when you start and once when you stop. So a hand timed measurement carries perhaps a fifth of a second of human error, which is twenty times anything the stopwatch contributes.

This is not a reason to distrust the number. It is a reason to know what the number is for. Hand timing is entirely adequate for training, cooking, experiments in a classroom, tracking how long a task really takes, and settling an argument. It is not adequate for an official race result, which is why sanctioned athletics uses electronic timing triggered by the starting gun and a beam at the finish rather than a person with a thumb.

One practical consequence: if you are comparing several laps to each other, your reaction time largely cancels out, because it is present in both ends of every lap. If you are comparing your time to someone else's, measured on a different device by a different person, it does not.

Switching away while it runs

Elapsed time is derived from the moment you pressed start, not accumulated while the page is watched. A browser will stop repainting a hidden tab, so the digits may sit still while you are elsewhere, but nothing is lost: the moment the tab is visible again the display catches up to the true reading on its first frame.

This is a genuine difference from a countdown, and worth understanding rather than taking on trust. A countdown has an alert to fire, so it has to keep working in a hidden tab or it fails completely, and the timers on this site are built accordingly. A stopwatch has nothing to announce. It only has to be right when you look, which it always is.

Getting the numbers out

The copy button puts the whole table on your clipboard as tab separated text, with lap, split and total in separate columns. Pasted into a spreadsheet it lands in the right cells without any cleaning up, which is the point: a stopwatch that gives you a table you then have to retype has not finished the job.

Laps do not survive a reload. That is on purpose. A stopwatch that silently restored a session from last Tuesday when you opened it expecting zero would cause more trouble than it saved, so the rule here is that reloading gives you a clean stopwatch and copying is how you keep anything.

When you want a different tool

A stopwatch counts up, with no end in mind. If you know how long something should take and want to be told when it is over, use the timer. If the pattern repeats, with work and rest alternating, the interval timer runs the rounds and beeps the last three seconds of each phase so you do not have to watch it. For focused work in sessions, the pomodoro timer handles the cycle and counts the rounds.