Sino-Korean Numbers: 일, 이, 삼, 사…

Korean runs two complete number systems side by side — the Sino-Korean set (borrowed centuries ago from Chinese) and the native Korean set. This page introduces the Sino-Korean numerals, the ones you will read off clocks, price tags, calendars, and phone screens all day long. The single most important idea to grasp on day one is this: you do not choose between the two systems by mood or formality. You choose by what you are counting. Sino-Korean is not "the polite one" or "the formal one" — it is the units-and-measures one. Get that framing right now and half the confusion evaporates.

Why Korean has two number systems

The twin systems are a legacy of centuries of borrowing from Chinese, and the closest thing English has to it is its own layered vocabulary. English keeps a homely Germanic word beside a learned Latinate one — ask / inquire, cow / beef, begin / commence. Korean did the very same thing with numbers: it kept its native count (하나, 둘, 셋…) for hands-on, everyday tallying, and borrowed the Sino set (일, 이, 삼…) for the "learned," measured, written-down domains — dates on a calendar, figures on a ledger, times marked on a clock. The two never fused; they split the territory. That's exactly why the choice feels arbitrary to English speakers at first — no single English distinction maps onto it — but the underlying rule is strikingly consistent: native for the tangible, Sino for the measured and abstract.

The ten building blocks

Every Sino-Korean number is built from just these:

(Zero has two words split by function — the value-zero 영 and the digit-string 공 — which get their own page: 영 vs 공.)

Building numbers by pure place value

The beauty of the Sino system is that it is fully regular. There are no "eleven / twelve" surprises. Ten is 십; eleven is literally "ten-one," 십일; twenty is "two-ten," 이십; twenty-three is "two-ten-three," 이십삼. Just read the places left to right.

Two small things to notice. First, one hundred is its own word, 백 — and in speech you say 백, not ×일백 (the leading "one" is dropped for 백, 천, 만). Second, when a batchim runs into the next digit you still spell each number plainly, but the pronunciation shifts: 십육 (16) is pronounced [심뉵] (simnyuk) — an inserted ㄴ triggers nasalization — while 육십 (60) is simply yuksip.

Where Sino-Korean numbers do their work

Sino-Korean is the system for the abstract and the measured: dates, money, minutes, phone and room numbers, floors, bus routes, math, and any large count. Here it is in its natural habitat.

The one reframing English speakers must internalize

Because English has a single set of numbers, learners instinctively treat the Sino set as the "default" and the native set as an exception. Flip that instinct. The two systems divide the labor by context, and the fault line runs right through everyday counting: concrete physical objects are counted with the native numbers, not Sino ones. Three apples is 사과 세 개 — the native 세 — and 사과 ×삼 개 sounds as wrong to a Korean ear as "the third apples" does to yours.

So the division looks roughly like this: Sino for dates, money, minutes, and measured/abstract counts; native for hours, ages, and counting tangible things. The native set gets its own page — start with native numbers and the system-by-counter guide.

There is one elegant escape hatch, though: above 99, even native-counted things switch to Sino. You count up to ninety-nine books with native numbers, but once you pass a hundred the native set runs out and Sino takes over. That switch — and the large place-words 만, 억, 조 — is the subject of the large-numbers page.

Common Mistakes

1. Using Sino numbers to count physical objects. The classic transfer error. Tangible things take native numbers plus a counter.

• ✗ 사과 삼 개
• ✓ 사과 세 개

2. Using Sino for the hour of the clock. Hours are native (세 시), but minutes are Sino (십오 분) — the clock mixes both systems in one breath.

• ✗ 삼 시 십오 분
• ✓ 세 시 십오 분

3. Adding 일 before 백 / 천 in speech. One hundred is 백, not ×일백; one thousand is 천, not ×일천.

• ✗ 일백 명
• ✓ 백 명

4. Mispronouncing 십육 (16). It is not sib-yuk; the standard pronunciation is [심뉵] (simnyuk), with an inserted ㄴ and nasalization. (60, by contrast, is a plain yuksip.)

5. Reading a phone-number 0 as 영. In a string of spoken digits, zero is 공, not 영 — 공일공, never ×영일영. See 영 vs 공.

Key Takeaways

• The Sino-Korean digits are 영/공, 일, 이, 삼, 사, 오, 육, 칠, 팔, 구, 십, and they build every number by transparent place value (십일 = 11, 이십삼 = 23, 백 = 100).
• Sino-Korean is the measured / abstract system: dates, money, minutes, phone numbers, floors, math, and counts of ~100 or more.
• The choice between Sino and native is decided by context, not formality — physical objects want native numbers (세 개), not Sino (×삼 개).
• Above 99, even native-counted things switch to Sino.