2都市間の時差計算
2つの地域やタイムゾーンの間の正確な時間差を計算します。
Compare two zones
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| Reference instant | Zone A | Zone B | B vs A |
|---|
仕組みと計算ルール
- Both zones’ offsets are resolved for the chosen date (sampled at 12:00 UTC), never assumed constant, because an offset is a property of a date, not a zone.
- The headline states the gap in hours and minutes with direction: "Tokyo is 9h ahead of London". Gaps of 30 or 45 minutes (India, Nepal, parts of Australia) are reported exactly.
- The table re-samples the same pair in mid-January and mid-July, so you can see whether the gap is stable all year or shifts with daylight saving.
知っておくと便利なポイント
- The difference is not always constant: zones on different DST schedules (or one with DST and one without) change their gap during the year, and the note explains when that applies.
- "Ahead" means a later wall time for the same instant: when it is 09:00 in London it is already 17:00 in Tokyo.
- Identical zones are detected and reported as such rather than pretending to compare.
関連ツール
よくある質問
Is the difference between two zones always constant?
No: if the zones observe DST on different schedules, the gap changes during the year. The tool compares offsets across seasons and highlights variations.
Why can the difference be 30 or 45 minutes?
Many zones use non-whole-hour offsets: India is UTC+05:30, Nepal is UTC+05:45, and parts of Australia use +09:30. The calculator reports the real minute-level gap.
What does “ahead” mean here?
Ahead means its wall clock shows a later time for the same instant. Tokyo is ahead of London; when it is 09:00 in London it is already 17:00 (or 18:00 in summer) in Tokyo.