世界時計
世界の主要都市の現在時刻をひと目で並べて確認できます。
Your world clock
No zones on the clock yet. Add one above.
| Zone | Time | Date | UTC offset | Day | Remove |
|---|
Up to 12 zones. The list is saved in this browser only and is never sent anywhere.
仕組みと計算ルール
- Each update re-reads the system clock and renders the current instant as wall time in every zone on your list; offsets are resolved per row, so daylight saving is always right.
- The "Day" column compares each zone’s calendar date with your own zone’s, marking previous day / next day so a date change never sneaks up on you.
- Your list is saved in this browser’s localStorage and restored on the next visit: no account and nothing transmitted.
知っておくと便利なポイント
- Up to 12 zones at once; remove rows individually.
- If storage is unavailable (such as in some private modes), the clock still works for the session; the list is simply not remembered.
- Cities sharing an IANA zone (e.g. New York and Boston) always show identical times by definition.
関連ツール
よくある質問
Is my city list sent anywhere?
No. It is saved only in your browser’s localStorage so it survives reloads. Clearing site data removes it; nothing is transmitted or synced.
Does the clock stay accurate in a background tab?
Yes. Each update reads the system clock fresh and the page resyncs when you return, so background throttling can never make the display drift.
Why is the same city listed under different zones?
The picker uses IANA zone identifiers, and some territories share a zone (for example, much of western Europe uses Europe/Paris); their clocks agree by definition.