Korean Numbers: When to Use Sino vs Native (and Why It Matters)
Korean has two complete number systems — Sino-Korean and native Korean. They're not interchangeable, and choosing the wrong one is one of the most common beginner mistakes. Here's how to never get it wrong.
Two Number Systems? Why?
Korean uses two parallel number systems and which one you pick depends entirely on what you are counting. Sino-Korean numbers (한자어 숫자) are borrowed from Classical Chinese and look like one-to-one matches with Japanese on'yomi readings: 일, 이, 삼, 사, 오, 육, 칠, 팔, 구, 십. Native Korean numbers (고유어 숫자) developed indigenously and have totally different roots: 하나, 둘, 셋, 넷, 다섯, 여섯, 일곱, 여덟, 아홉, 열.
Korean is unusual but not unique in having two systems. Japanese has the same situation (一・二・三 vs ひとつ・ふたつ・みっつ), and the rules for choosing between them in Japanese are similar but not identical to Korean's rules. If you are coming from Japanese, the conceptual framework is familiar — you have already lived with this complication — but the specific allocation of which system goes with which counter is different enough that you cannot simply translate.
The reason both systems survive is that they grew separately and each has historical territory. Sino-Korean handles abstract counting, time, dates, money, and large numbers. Native Korean handles smaller counts, ages, hours (but not minutes), and everyday quantities. The split is not random; once you learn the categories, you will not mix them up.
When to Use Sino-Korean Numbers
Use Sino-Korean for dates and time when you are not counting hours. Months use Sino-Korean: 일월 (January), 이월 (February), 삼월 (March). Days of the month use Sino-Korean: 일일 (1st), 이십오일 (25th). Years use Sino-Korean: 이천이십육년 (year 2026). Minutes use Sino-Korean: 삼십분 (30 minutes).
Use Sino-Korean for money. 천 원 (1,000 won), 만 원 (10,000 won), 십만 원 (100,000 won). Large monetary amounts use the Sino-Korean place-value system, including the distinctive Korean convention of grouping by 만 (10,000) rather than by 1,000.
Use Sino-Korean for phone numbers, addresses, room numbers, and most identification numbers. 공일공-이삼사오-육칠팔구 ('010-2345-6789'). Use Sino-Korean for floor numbers in buildings (이층 = 2nd floor) and for grades in school (삼학년 = 3rd grade). Use Sino-Korean for any abstract or scientific counting — 백 (100), 천 (1,000), 만 (10,000), 억 (100 million).
When to Use Native Korean Numbers
Use native Korean for hours when telling time. 한 시 (1 o'clock), 두 시 (2 o'clock), 세 시 (3 o'clock). The minutes that follow use Sino-Korean: 세 시 삼십 분 (3:30). This mixed system is unintuitive at first but quickly becomes automatic.
Use native Korean for age. 스무 살 (20 years old), 서른 살 (30 years old). Until recently, age in Korea was calculated by the traditional Korean reckoning where you are 1 at birth and add a year every January 1st, leading to confusing 'Korean age vs international age' conversations. In 2023, Korea officially standardised on international age, but in casual conversation Koreans still sometimes default to traditional age — clarify if it matters.
Use native Korean for counting people and most concrete objects with their associated counter words. 사람 두 명 (two people), 강아지 세 마리 (three dogs), 책 네 권 (four books), 사과 다섯 개 (five apples), 커피 한 잔 (one cup of coffee). Native Korean numbers are used with the counter; Sino-Korean numbers are used for the abstract count alone.
The Modification Trick
When native Korean numbers 1, 2, 3, 4, and 20 modify a counter (come before a counter word), they take shortened forms. 하나 becomes 한, 둘 becomes 두, 셋 becomes 세, 넷 becomes 네, 스물 becomes 스무. So you say 한 시 (1 o'clock), not 하나 시. You say 두 명 (two people), not 둘 명. You say 스무 살 (20 years old), not 스물 살.
All other native Korean numbers stay the same when modifying. 다섯 시 (5 o'clock), 일곱 명 (seven people), 열 권 (ten books). The modification rule applies only to 1, 2, 3, 4, and 20.
Why these particular numbers? Linguistically, they descend from older forms where the modifier function was distinguished morphologically. You do not need to know the history, but you do need to learn the five exceptions as a single block — they are extremely common and using the long form sounds noticeably non-native.
Counter Words: The Hidden Layer
Korean (like Japanese and Chinese) uses counter words for almost every category of object. You do not say 'three books'; you say 'books three 권' (책 세 권), where 권 is the counter for bound objects. The counter word category depends on what you are counting and the number is native Korean.
Some common counters: 명 (people), 마리 (animals), 권 (books), 개 (general objects), 잔 (cups/glasses), 병 (bottles), 장 (sheets of paper), 대 (machines/vehicles), 송이 (flowers), 켤레 (pairs of shoes/socks).
When you do not know the specific counter for an object, 개 is the universal fallback. 두 개 ('two pieces') works for almost any concrete object. Native speakers will understand even when 개 is not the most precise counter, and using 개 by default in a pinch is far better than using no counter at all.
Numbers in Time: The Mixed System That Trips Everyone
Time of day in Korean famously mixes the two number systems. The hour uses native Korean numbers (with the modification rule): 한 시 (1:00), 두 시 (2:00), 세 시 (3:00) ... 열두 시 (12:00). The minutes use Sino-Korean: 오 분 (5 minutes), 십오 분 (15 minutes), 삼십 분 (30 minutes). Combined: 세 시 삼십 분 (3:30).
AM and PM are 오전 (AM, Sino-Korean) and 오후 (PM, Sino-Korean). Native Korean does have words for morning and afternoon (아침, 오후), but the formal AM/PM markers used in announcements and writing are Sino-Korean. 오전 열한 시 (11 AM), 오후 세 시 (3 PM).
Duration in hours uses native Korean: 두 시간 (for two hours, duration). Compare with 두 시 (at 2 o'clock, point in time). The same number word but with different counters and slightly different meaning. This pattern of native-for-hours / Sino-for-minutes is consistent and worth memorising as a unit.
Practical Memory Strategies
If you are coming from Japanese, your existing knowledge of when to use 一・二・三 vs ひとつ・ふたつ・みっつ gives you almost the right calibration for Korean — the rules differ in details but the conceptual frame is identical. Trust your intuition for the time-and-money domain (Sino) versus the counting-objects-with-counters domain (native), and treat the Korean-specific differences as small adjustments.
If you are coming from English, the most efficient learning order is: master 1-10 in native Korean first (because you'll use them with counters from day one), then master 1-10 in Sino-Korean (because you'll need them for time, money, and dates), then memorise the modification forms 한/두/세/네/스무, then learn the counter words one at a time as they come up in lessons.
Do not try to learn both systems' large numbers simultaneously. Korean only uses native numbers up to 99; beyond 100 everything is Sino-Korean. So your effort on 'big numbers' should focus entirely on Sino-Korean, while your native-number learning effectively stops at 99. This split saves significant memorisation effort.
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