Time events with a stopwatch on Apple Watch
Time events with accuracy and ease. Apple Watch can time full events (up to 11 hours, 55 minutes) and keep track of lap or split times, then show the results as a list, a graph, or live on your watch face. The Chronograph and Chronograph Pro watch faces have the stopwatch built in.
Open a stopwatch
Open the Stopwatch app 
on your Apple Watch, or tap the stopwatch on your watch face (if you’ve added it or you’re using the Chronograph or Chronograph Pro watch face).
Start, stop, and reset the stopwatch
Open the Stopwatch app on your Apple Watch, then do any of the following:
Start: Tap the green Start button.
Record a lap: Tap the white Lap button.
Record the final time: Tap the red Stop button.
Reset the stopwatch: Tap the white Reset button or the Lap button.
The timing continues even if you switch back to the watch face or open other apps.
Review results on the display you used for timing, or change displays to analyze your lap times and fastest/slowest laps (marked with green and red) in the format you prefer. If the display includes a list of lap times, turn the Digital Crown to scroll.
Change the stopwatch format
Open the Stopwatch app
on your Apple Watch.Tap the display to cycle through Digital, Analog, Graph, and Hybrid formats.