The difference between 일 and 한 to mean "one"?

Question

It seems that one month, one week, and one year in Korean are the following:

한 달 (one month)

한 주 (one week)

일 년 (one year)

Why do the first two use '한' while the last one uses '일'? And how can I classify them if I encounter a new word?

Answer 1

It's complicated... sometimes you can even use both and it changes either the meaning or style of speech.

The book Using Korean devotes an entire chapter (about 9 pages) to this topic. Read the full details and numerous examples starting from page 169.

I'll try to summarize below (all quotes from Using Korean, examples have been greatly abridged):

General summary

In most cases, there is a strict division of labor in the use of native Korean numbers and Sino-Korean numbers. For example, native Korean numbers are used for counting (small numbers) and for o'clock (세시 "3 o'clock"), while Sino-Korean numbers are employed for minutes, dates, months, years, money, and so forth (16 절지 '8.5 by 11 size paper', 24 금 '24 K gold', and so on).

 

In some cases, both types of numbers can occur with the same counter, creating sharp contrasts in meaning.

• 다섯 번 five times (quantity)
• 오 번 number 5 (order)

 

Very rarely, either number can be used for the same concept, but this is correlated with a contrast in speech style.

• 스무 살 20 years old (colloquial)
• 이십 세 20 years old (written/formal)

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Counting

Native numerals are used for counting smaller units. For larger quantities, Sino-Korean numerals are used, often in combination with native numbers. There is a tendency for Sino-Korean numbers to be used for multiples of 10, starting from 20, even when there is a native Korean counterpart.

• 1: 종이 한 장 one sheet of paper
• 10: 종이 열 장
• 20: 종이 스무 장 or 이십 장
• 125: 종이 백 스물 다섯 장 or 백 이십 오 장

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Units of measurement

Sino-Korean numbers are used for the metric system as well as some American units of measurement. Native numbers are employed only for a few traditional Korean units of measurement.

Time, date, and age

Both native and Sino-Korean numerals can be used for times, dates, and ages. A particularly notorious case involves telling time, which requires a native number for o'clock but a Sino-Korean number for minutes.

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Arithmetic and fractions

Sino-Korean numbers are used for arithmetical calculation, fractions (분수), decimals (소수), and multiplication tables (구구단). But native numbers are used for numerical comparison in general.

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Money and Currency, Numbers relating to transportation

Sino-Korean numbers are used.

Answer 2

일 is not quantitative, in other words you should use 일 whenever you are not counting. So for example, telephone numbers, IDs, use 일 instead of 한.

Example: 일 항 -> paragraph one

한 is opposite, it is used only when you are counting.

Example: 한 마디 -> one sentence,

한 사람 -> one person

However, if there is no counter, use 하나 instead. Ex: 하나 있다 -> There is one

There are some exceptions, when 일 is used instead of 한(하나): 년, 초, 분, 주, 일, 개월.

There are still some others, but rarely will it happen, so just memorize them if you encounter one.

So in your example, 한 주 is wrong, but 일 주.

Correct me if I am wrong.