Why Koreans use 이틀 (2 days) 사흘 (3 days) instead of 이일 and 삼일 | 1 day, 2 days, 3 days in Korean
- KSJ 쌤
- 4 days ago
- 3 min read
안녕하세요 여러분! It's Koreanstudyjunkie here. I've been wondering for a long time why we must use words like 하루, 이틀, 사흘 to say 1 day, 2 days, 3 days instead of 일일, 이일, 삼일.
Today, let's do a deep dive on the topic!
In Korean, both sets of words— 하루, 이틀, 사흘 and 일일, 이일, 삼일—are used to express durations of days, but they have different nuances and usage patterns.
Native vs. Sino-Korean Numbers
하루, 이틀, 사흘, 나흘,... → Native Korean words
일일, 이일, 삼일, 사일,... → Sino-Korean words (from Chinese)
Korean has two numbering systems:
Native Korean numbers (used for counting things, age, and durations)
Sino-Korean numbers (used for dates, formal contexts, and technical terms)
Them being from different number systems means the usage is automatically different!
What’s The Difference?
NATIVE KOREAN (하루, 이틀, 사흘..,)
Used more commonly in daily conversation
Applies to 1 to 10 days
Sounds more natural and traditional in storytelling, daily speech, and informal settings
Common in idioms and expressions
Native Korean words like this only are used up to 나흘 (4 days). For 5 days and beyond, Koreans switch to the Sino-Korean system (오일, 육일, etc.).
There’s no pure Korean word for "5 days" like "다섯흘"— it doesn’t exist in standard Korean, although you may see words like 닷새 (5 days) or 엿새 (6 days), they aren't often used.
Example: 다섯흘 동안 여행했어요. (Incorrect) 오일 동안 여행했어요. (Correct)
Vocab To Know:
하루 - 1 day
이틀 - 2 days
사흘 - 3 days
나흘 - 4 days
Example Sentences:
하루 종일 집에 있었어요.
=I stayed home all day.)
이틀 동안 여행 갔어요.
= I went on a trip for two days.
사흘 후에 돌아올게요.
= I will return in three days.
나흘 동안 아무 연락도 없었어.
= There was no contact for four days.)
SINO-KOREAN (일일, 이일, 삼일...)
Used in official, formal, or written contexts
Dates & specific day mentions (e.g., 3rd day of the month)
Easier to extend beyond 5 days (e.g., 십오일 = 15 days)
Example Sentences:
삼일 동안 회의가 있어요.
= There is a meeting for three days.
시험이 이일 남았어요.
= Two days left until the exam.
이일 동안 배송될 예정입니다.
= The delivery will take two days.
오늘은 3월 1일이에요.
= Today is March 1st.
Idioms and Expressions Using These Words
1. 하루 (1 day) Idioms
하루 아침에 → "Overnight" (something happening suddenly)
Example: 그의 사업이 하루 아침에 망했어요. = His business failed overnight.
하루가 다르게 → "Changing day by day"
Example: 아이들이 하루가 다르게 자라고 있어요. = The children are growing day by day.
2. 이틀 (2 days) Idioms
이틀 걸러 한 번 → "Every other day"
Example: 그는 이틀 걸러 한 번씩 운동해요. = He works out every other day.
3. 사흘 (3 days) Idioms
사흘 굶어 도둑질 안 하는 사람 없다 → "No one can go three days without food and not steal" (Hunger drives people to desperate actions)
Example: 너무 배고프면 사흘 굶어 도둑질 안 하는 사람 없다는 말처럼 사람도 변할 수 있어요. = If you're too hungry, even an honest person can change, as the saying goes.
4. 나흘 (4 days) Idioms
나흘이나 걸렸다 → "It took four whole days" (Emphasizing a long time)
Example: 이 책을 읽는 데 나흘이나 걸렸어요. = It took me four whole days to read this book.
That's all for this post! Thanks for reading if you made it this far. Below this lesson, I have linked 3 other related-lessons to expand your Korean knowledge ;)
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