Online Stopwatch

This online stopwatch counts up from zero in minutes, seconds and hundredths of a second, and records lap splits while it runs. Press Start to begin, Lap to capture a split and Reset to clear everything. It suits track and pool sessions, speech rehearsals, cooking and school science practicals.

The controls

• Start / Pause: one button. Once running it reads Pause; press it to freeze the time and again to carry on from the same point.
• Lap: available only while the stopwatch is running. Each press adds a line to the Laps list.
• Reset: stops the clock, sets it back to zero and clears all laps.

The display reads like 2:05.37, meaning 2 minutes and 5.37 seconds. After an hour it adds an hours field, as in 1:02:05.37.

Laps are split times

Each entry in the Laps list is the total time on the clock at the moment you pressed Lap, known as a split. The newest appears at the top, so Lap 3 sits above Lap 2. To get the time for an individual lap, subtract the previous split. Three laps of a 400 m track might look like this:

Here the runner slowed on lap 2 and recovered on lap 3, which the splits alone make hard to see.

How accurate is it?

The elapsed time is worked out from your device's clock, as the difference between now and the moment you pressed Start, rather than by counting ticks. That keeps it correct even if the tab sits in the background or the screen stutters. The display refreshes roughly 23 times a second, so the hundredths digit jumps between values instead of rolling through every one, but the time behind it is precise.

The bigger source of error is the person pressing the button. Human reaction time is around a fifth of a second or more, so for fair comparisons let the same person start and stop every attempt, and react to the same cue each time.

Useful ways to time things

• Simple pendulum practical: time 20 complete swings and divide by 20. Your reaction delay is spread across all the swings instead of spoiling a single one.
• Speech or viva practice: press Lap at the end of each section to see which part runs long.
• Interval training: press Lap at the end of each sprint and read the recovery gaps from the splits.
• Task timing: measure how long routine jobs actually take before quoting a client for them.

Limits

Laps are not saved: refreshing or closing the page loses them, and there is no export, so note them down before you reset. For a timer that counts down and beeps at the end, use the countdown timer; to add or subtract recorded times, the time duration calculator helps. The stopwatch runs entirely in your browser.