Korean has two number systems. This surprises most learners. You need both. They're used in completely different contexts and you can't mix them up.
The two systems
Sino-Korean (한자어): Based on Chinese numerals. Used for dates, money, phone numbers, addresses, minutes, and anything over 100.
Native Korean (고유어): The original Korean numbers. Used for counting objects (with counters), age (informally), hours on a clock, and quantities up to 99.
The numbers side by side
| Number | Sino-Korean | Native Korean |
|---|---|---|
| 1 | 일 (il) | 하나 (hana) |
| 2 | 이 (i) | 둘 (dul) |
| 3 | 삼 (sam) | 셋 (set) |
| 4 | 사 (sa) | 넷 (net) |
| 5 | 오 (o) | 다섯 (daseot) |
| 6 | 육 (yuk) | 여섯 (yeoseot) |
| 7 | 칠 (chil) | 일곱 (ilgop) |
| 8 | 팔 (pal) | 여덟 (yeodeol) |
| 9 | 구 (gu) | 아홉 (ahop) |
| 10 | 십 (sip) | 열 (yeol) |
| 20 | 이십 (isip) | 스물 (seumul) |
| 30 | 삼십 (samsip) | 서른 (seoreun) |
| 100 | 백 (baek) | . |
| 1,000 | 천 (cheon) | . |
Native Korean stops being used at 100. Everything above 99 uses Sino-Korean.
When to use which
Use Sino-Korean for:
- Dates: 4월 10일 (April 10th) → 사월 십일
- Money: 3,000원 → 삼천 원
- Phone numbers: each digit individually
- Minutes: 30분 (30 minutes) → 삼십 분
- Floor numbers: 5층 (5th floor) → 오층
- Percentages, measurements
Use Native Korean for:
- Counting objects with counters: 사과 두 개 (two apples). 두 is the modified form of 둘
- Hours on the clock: 세 시 (3 o'clock). 세 is modified form of 셋
- People: 세 명 (three people)
- Age (informal): 스물다섯 살 (25 years old)
The modified forms
When native Korean numbers come before a counter, some change form:
| Original | Before counter |
|---|---|
| 하나 | 한 |
| 둘 | 두 |
| 셋 | 세 |
| 넷 | 네 |
| 스물 | 스무 |
So: 한 개 (one thing), 두 명 (two people), 세 시 (three o'clock).
Quick test
- "It's 2 o'clock" → 두 시 (native, hours)
- "It costs 2,000 won" → 이천 원 (Sino, money)
- "I have 2 apples" → 사과 두 개 (native + counter)
- "Today is the 2nd" → 이일 (Sino, date)
The fastest way to drill this is through repetitive exposure with immediate feedback. A structured Korean course has number-specific drills that mix both systems so you develop automatic recall.