Digital Clock with Seconds
A large, easy-to-read clock that shows the exact time down to the second. Choose 12 or 24 hours and any time zone, go full screen, and check how accurate your device clock is.
How to use the Digital Clock with Seconds
- Read the time: the clock starts right away in your device's time zone.
- Pick 12h or 24h and, if you like, tenths of a second and the date.
- Choose a time zone to see the exact time anywhere in the world.
- Press Check sync to compare your device clock with the server's clock and see the offset.
- Go full screen for a big bedside, desk or classroom clock. Press Esc to exit.
How the clock sync check works
Every web server stamps its replies with a Date header in whole seconds. The tool sends four quick requests and, for each one, notes the local time just before it was sent (t₀) and just after the reply arrived (t₁). If the header says D, the server's clock was somewhere between D and D + 1 s while the request was in flight, so the offset must lie in the range:
D − t₁ ≤ offset ≤ D + 1 s − t₀
Each sample catches the server's second ticking over at a different moment, so intersecting the four ranges narrows the answer down. The middle of the final range is the offset and half its width is the uncertainty. With a 40 ms round trip you typically get a result within about ±0.3 s.
A negative offset means your device clock is ahead of the server; a positive one means it is behind.
12-hour and 24-hour time
| 24-hour | 12-hour | 24-hour | 12-hour |
|---|---|---|---|
| 00:00 | 12:00 AM (midnight) | 12:00 | 12:00 PM (noon) |
| 01:00 | 1:00 AM | 13:00 | 1:00 PM |
| 06:30 | 6:30 AM | 18:30 | 6:30 PM |
| 09:15 | 9:15 AM | 21:15 | 9:15 PM |
| 11:59 | 11:59 AM | 23:59 | 11:59 PM |
Keeping your device clock accurate
- Windows: Settings › Time & language › Date & time › turn on "Set time automatically" and press "Sync now".
- macOS: System Settings › General › Date & Time › turn on "Set time and date automatically".
- iPhone and iPad: Settings › General › Date & Time › "Set Automatically".
- Android: Settings › System › Date & time › "Set time automatically" (or "Use network-provided time").
Computers sync with time servers using NTP, which is accurate to a few milliseconds. If the sync check keeps showing an offset of more than a second, automatic time is probably turned off.
Frequently asked questions
How accurate is this clock?
It shows your device's clock, which is normally synchronized with internet time servers and is accurate to a fraction of a second. The sync check compares it with the web server's clock and tells you if it is off.
How does the sync check work?
The page asks the web server for its current time a few times and reads the Date header of each reply. Because that header only has whole seconds, the tool combines several samples and the round-trip time into an offset with an uncertainty range, usually within half a second.
Why is my clock a few seconds off?
Automatic time sync may be turned off, the device may have been asleep, or the network time server may be unreachable. Turn on 'Set time automatically' in your system settings. You can also tick 'Correct the display' so this page shows the server time.
Can I show the time in another time zone?
Yes. Pick any city zone from the list. The clock uses your browser's built-in time zone database, so daylight saving time changes are handled automatically.
Will the screen stay on in full screen mode?
Where the browser supports the Screen Wake Lock API, full screen mode asks it to keep the screen awake. Otherwise your device's normal sleep settings apply.
Does this clock work offline?
Yes. Once loaded it runs entirely in your browser. Only the optional sync check needs a connection.