How to use the stopwatch
- Start (or press Space) counts up from 00:00.00 in minutes, seconds and hundredths. After one hour the display adds hours, for example 1:00:00.00.
- Lap (or L) records a lap while the stopwatch runs. Each row shows the lap number, its Lap time and the Total time, newest on top. From the third lap on, the fastest lap is marked green and the slowest red, with a label.
- Stop (Space again) pauses the clock, and Start carries on from the same time.
- Reset (or R) clears the time and every lap. It is switched off while the clock runs so you cannot wipe a run by accident.
- Copy laps puts the table on the clipboard as tab-separated text that pastes into a spreadsheet.
How lap and total time are worked out
The stopwatch reads performance.now(), the browser's high-resolution clock, which keeps counting steadily even if the computer's clock is changed. If a phone or laptop sleeps while the stopwatch runs and the browser clock pauses with it, the system clock shows more time than the browser clock, and the stopwatch adds the difference back. Time is stored in whole hundredths of a second. The total is the time since you pressed Start, minus any time spent stopped. A lap time is the difference between this lap's total and the previous lap's total (or zero for the first lap), so the lap times always add up exactly to the last total.
Worked example
A runner presses Lap after 1:00.00, 2:05.00 and 3:03.00 on the clock. The table shows Lap 1 as 01:00.00 and 01:00.00, Lap 2 as 01:05.00 and 02:05.00, and Lap 3 as 00:58.00 and 03:03.00. Lap 3 is marked fastest and Lap 2 slowest. Check: 60 + 65 + 58 seconds is 183 seconds, which is 03:03.00.
Limits and edge cases
- Reloading or closing the page clears the time and the laps. Nothing is saved or sent anywhere.
- The display rounds down to the hundredth, so it never shows a time that has not happened yet.
- Lap works only while the clock runs, and Reset only while it is stopped.
- For a countdown that rings at zero, use the countdown timer. For repeating work and rest rounds, try the interval timer or the Tabata timer, and to measure your reflexes use the reaction time test.
Frequently asked questions
What is the difference between lap time and split time?
A lap time is the time for one segment, from the previous lap button press (or the start) to this one. A split time is the running total from the start, shown here as Total time. If three laps take 1:00, 1:05 and 0:58, the splits are 1:00, 2:05 and 3:03.
How accurate is an online stopwatch?
The clock itself is accurate to about a millisecond, and the display shows hundredths of a second. In practice your reaction time, around 0.2 seconds when you press the button, is the larger error. It is fine for workouts, cooking, study and speeches, but not for official race timing.
What is the difference between a stopwatch and a timer?
A stopwatch counts up from zero to tell you how long something took. A timer counts down from a time you set and alerts you at zero. Use a stopwatch to measure, and a countdown timer when you need to be told that time is up.
Does the stopwatch keep running if I switch tabs?
Yes. The elapsed time is read from the clock each time the display updates, not counted in ticks, so a background tab stays correct. If your device sleeps or locks, the stopwatch catches up from the system clock when the page wakes. Closing or reloading the page clears it, so keep the tab open.
Which keyboard shortcuts does the stopwatch use?
Press Space to start or stop, L to record a lap and R to reset. Reset only works while the stopwatch is stopped, so a stray key press cannot wipe a run in progress. Shortcuts are ignored while you type in a field and when Ctrl, Alt or Command is held.