What is an online stopwatch?
A stopwatch measures elapsed time from the moment you start it until you stop it. Unlike a timer, which counts down, it counts up, so it suits activities where you do not know the length in advance: a run, a speech, a science experiment, a cooking step or a work task you want to time honestly.
This stopwatch shows hours, minutes, seconds and milliseconds and supports lap times. It runs in your browser on phones and computers and needs no download.
How it keeps accurate time
Many web timers add a fixed amount on every tick, which drifts when the browser is busy. This stopwatch stores the moment you pressed Start and works out the elapsed time from your device clock every time it redraws, so the result stays correct even when the page slows down or you switch tabs.
A lap records the total time at the moment you press Lap without stopping the clock. To find the length of one lap, subtract the previous lap time from the current one. For example, laps at 1:05.200 and 2:12.700 mean the second lap took 1:07.500.
How to use it
- Press Start or the Space bar to begin.
- Press Lap (or L) to record a split while the clock keeps running.
- Press Stop to pause, and Start again to continue from the same time.
- Press Reset (or R) to clear the time and all laps. Press F for full screen.
Practical tips
- Runners and swimmers can record a lap at the end of every length or kilometre and compare them to see where they slow down.
- Teachers can use full screen on a projector so the whole class sees the time.
- Time yourself on a task such as typing or revision to learn how long things really take.
- Write down laps before pressing Reset, because they are not saved.
Frequently asked questions
What is the difference between a stopwatch and a timer?
A stopwatch counts up from zero. A timer counts down from a time you choose.
How accurate is it?
It shows milliseconds and measures real elapsed time from your device clock.
Will it keep running in another tab?
Yes. The time is calculated from the clock, so it is correct when you return.
Are my laps saved?
No. They disappear when you reset or leave the page.
Does it work on my phone?
Yes. The layout adapts to small screens and the buttons are easy to tap.