Set an alarm, start a timer, record lap times or check the time around the world. You can also convert between 12-hour and 24-hour time or find a countdown to an upcoming event.
Learning guide
What you’ll learn
Measure elapsed time, convert clock formats, and compare local times.
What to change
Set a duration, enter start and end times, or choose locations.
What to observe
Compare elapsed time, equivalent clock readings, and local times.
Why it happens
Different clock formats can represent the same time. Time zones use different offsets to determine local time.
Teacher notes
Learning objective: Measure an interval or compare two representations of time.
Suggested ages: 9–14. Adapt the activity to your group.
Suggested duration: 5–10 minutes for one activity.
Prerequisite knowledge: Read a clock and understand hours, minutes and seconds.
Common misconception: Confusing noon and midnight. In 12-hour notation, 12 a.m. is midnight and 12 p.m. is noon.
Sources and methodology: Read our methods and data sources, including browser timing and time zones.
Tool limitations: Clock readings depend on your device’s time and time-zone data. Closing the tab, putting the device to sleep or muting sound can prevent an alarm from being heard. Check each tool’s instructions before using it in class.
Lesson status: These are classroom tools and short exploration activities. Ages and durations are suggestions, not classroom-tested results. Lesson development and unfinished drafts are separate.
Open to see the full screen bedside clock.
- Lap 300:04.5100:12.47
- Lap 200:03.8600:07.96
- Lap 100:04.1000:04.10
What is the International Date Line? The International Date Line is an imaginary boundary, mostly through the Pacific Ocean, where the calendar date changes.
8h 00m
Full time difference calculator →What is daylight saving time? Daylight saving time moves clocks forward, usually by one hour, for part of the year.
24-hour clock
18:40
12-hour clock
6:40 PM
Said aloud: “eighteen forty” on the 24-hour clock, “six forty in the evening” on the 12-hour one.
Explore 12-hour and 24-hour time →Event countdowns
Live countdowns to birthdays, holidays, sports and the days you're waiting for.
Keep exploring timers, stopwatches, world clocks and time conversion. Or jump across: All · Earth · Space.