十二時辰怎麼對應現在的時間？子丑寅卯一次看懂

How do the twelve earthly branches map to clock hours?

作者：Wei Chun Chuang・2026-10-24

Any Bazi chart asks what time you were born, because the hour pillar depends on it. The traditional day is divided into twelve double-hours, each named after an earthly branch. This article gives the order, the full mapping to clock time and the Zi-hour problem that trips people up.

The order of the twelve branches

There are twelve branches, always in this order: Zi, Chou, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu, Hai. They are used to label years and months as well as hours. Used for hours, one round covers exactly one day.

Why is one branch two hours?

Twenty-four hours divided among twelve branches gives each branch two hours. Traditional timekeeping had no minute hand, and this coarser unit was enough. Converted to a modern clock, each branch spans two whole clock hours.

The twelve double-hours

• Zi 23:00–01:00
• Chou 01:00–03:00
• Yin 03:00–05:00
• Mao 05:00–07:00
• Chen 07:00–09:00
• Si 09:00–11:00
• Wu 11:00–13:00
• Wei 13:00–15:00
• Shen 15:00–17:00
• You 17:00–19:00
• Xu 19:00–21:00
• Hai 21:00–23:00

Note the Zi hour: it does not start at midnight but at 11 p.m. the previous evening, running through midnight to 1 a.m. The other eleven branches sit inside a single calendar day; only Zi is cut in half by midnight.

Early Zi and late Zi: schools disagree

Because midnight splits the Zi hour, a question follows: which day does the stretch from 11 p.m. to midnight (often called late Zi or night Zi) belong to?

1. One view holds that the day begins with the Zi hour, so the day changes at 11 p.m. and the day pillar advances immediately.
2. Another view changes the day at midnight, so 11 p.m. to midnight still belongs to the outgoing day and the day pillar does not move.

Both have textual support, and this article does not pick one. The practical effect is concrete: for a birth between 11 p.m. and midnight, the two rules produce different day pillars, hence a different Day Master, and every Ten Gods relationship in the chart shifts with it. If you were born in that window, find out which rule your tool applies and what the other rule would give.

The hour branch fixes the hour pillar

In the hour pillar, the branch is the branch of the birth double-hour, and the stem is derived from the day stem. So an uncertain birth time means an uncertain hour pillar. This deserves honesty: a relative's memory of "around daybreak" or "not long after dinner" is approximate and cannot pin a branch down. Without a reliable recorded time, the reasonable move is to read only the year, month and day pillars rather than treating a guessed hour as fact.

Are the zodiac animals the same branches?

They are the same twelve branches, each paired with an animal: Zi rat, Chou ox, Yin tiger, Mao rabbit, Chen dragon, Si snake, Wu horse, Wei goat, Shen monkey, You rooster, Xu dog, Hai pig. The difference is that the animal people normally quote comes from the year branch, while an hour is the hour pillar's branch. Someone can be born in a rabbit year during the Wu hour; the year branch and the hour branch need not match.

What else matters when converting a recorded time

A time on a household record or hospital note is clock time, and clock time is a convention:

• Standard time zones: apparent solar time differs across a single time zone. Some schools correct to mean solar time using the birth longitude; others simply use the clock reading.
• Daylight saving: Taiwan observed summer time in several periods, when clocks ran an hour ahead. Without restoring that, the branch can land one slot off.
• Birthplace: the conversion needs a location, not just a time. The same clock reading means a different sun position at a different longitude.

Supplying a Gregorian date, a time and a birthplace is therefore far more reliable than a time alone.

常見問題

Born at 11:30 p.m. — is that the Zi hour or the previous day?

The hour branch is Zi either way, but schools differ on whether the day pillar advances: some change the day at 11 p.m., others at midnight. Check which rule your tool uses.

Can you build a chart without a birth time?

The year, month and day pillars can still be worked out, but the hour pillar stays unknown. Some tools let you pick an hour to experiment with, but that is an assumption, not your hour pillar.

Are the zodiac animals the same twelve branches?

Yes, they are the same twelve branches, but the animal people quote is the year branch. Someone born in the Wu hour has Wu (Horse) as the hour branch, which need not match their year animal.

Practise with an app

To see how your own double-hour becomes an hour pillar, Shilai – Bazi is an iPhone course that teaches you to read Bazi, with the four pillars calculated for you. It is currently in App Store review and not yet released, so it cannot be downloaded. In the meantime the free web version builds a chart with no sign-up or login and includes 20 lessons you can read alongside the hour table.

更多入門文章