Online stopwatch

Use the stopwatch when you want to measure how long an activity takes rather than count down to a deadline. Before you begin, decide if you need a single elapsed time or separate laps for repeated tasks.

1. Select Stopwatch to use the stopwatch.
2. Choose Full screen if you want only the tool visible on your projector or smartboard.
3. Select Start when the activity begins.
4. Select Lap at each checkpoint to record a lap time and total time.
5. Select Pause when you want to stop timing, then use Copy laps to copy the recorded laps as text.
6. Use Reset when you are ready to begin a new timing session.

The stopwatch measures elapsed time and displays minutes, seconds, and hundredths, adding hours after the first hour. Each recorded lap includes its lap time and the total elapsed time. A hundredths display is not a guarantee that every classroom start or finish is measured to that precision.

The browser’s high-resolution timing API provides timestamps measured in milliseconds. Its clock is monotonic: it does not go backward or change with adjustments to the system clock. Browser security settings can reduce its timing resolution, and ticking during computer sleep differs across operating systems, so avoid relying on a sleeping computer for timing.

For keyboard control, Space starts and pauses the stopwatch, L records a lap, R resets, and F opens full screen. You can use these shortcuts while watching the activity instead of moving the pointer between controls. The stopwatch records up to 99 laps and marks the fastest and slowest once you have 3 laps.

Choose the stopwatch when the question is how long something takes. Agree on the start and finish points before timing, especially when you plan to compare repeated attempts.

• Classroom transitions: start as the class begins putting materials away and pause when everyone is ready for the next activity.
• Science observations: start at the beginning of a demonstration and record a lap at each visible change, continuing until the observation ends.
• Small-group presentations: time each group from its opening to its finish, then copy the lap record for your lesson notes.
• Independent study: let the clock run during a work session and record a lap whenever the class moves to a different task.