Why Korean Uses Two Number Systems

You step into a cozy café in Seoul, the aroma of roasted coffee beans filling the air. You’ve practiced your line. “Keopi han jan, juseyo,” you say, asking for “one cup of coffee.” The barista smiles. A few hours later, a friend asks you for the time. You glance at your watch—it’s 2:30. “Du-si sam-sip bun,” you reply. In just a few hours, you’ve used two completely different ways to say “one,” “two,” and “thirty.”

Welcome to one of the most famously tricky, yet fascinating, aspects of the Korean language: its dual number system. For learners, it can feel like a confusing hurdle. But this system isn’t just a random quirk; it’s a living linguistic fossil, a direct reflection of Korea’s unique history and its deep, centuries-long relationship with its neighbors.

Let’s unravel the why and how of Korea’s two sets of numbers.

Meet the Players: Native Korean vs. Sino-Korean

First, let’s get acquainted with the two systems. Every number in Korean from 1 to 99 has two different forms. (Don’t worry, it gets simpler after 100!)

The Native Korean System

These are the original, homegrown Korean numbers. They’ve been a part of the Korean language since its earliest days. Think of them as the “counting” numbers.

• One: 하나 (hana)
• Two: 둘 (dul)
• Three: 셋 (set)
• Four: 넷 (net)
• Five: 다섯 (daseot)
• Ten: 열 (yeol)
• Twenty: 스물 (seumul)

This system is primarily used for counting tangible, physical objects, people, and actions. It’s the one you’ll use for ordering items, telling your age, and counting hours.

The Sino-Korean System

As the name suggests, the Sino-Korean system has its roots in Chinese. These numbers were adopted from Middle Chinese and their pronunciations were adapted over centuries to fit Korean phonology. Think of them as the “measuring” or “labeling” numbers.

• One: 일 (il)
• Two: 이 (i)
• Three: 삼 (sam)
• Four: 사 (sa)
• Five: 오 (o)
• Ten: 십 (sip)
• Twenty: 이십 (isip)

This system is used for more abstract or systematic concepts: money, dates, phone numbers, minutes, math, and anything numbered above 100.

A Tale of Two Languages: The Historical “Why”

So why did Korea end up with two systems instead of just sticking with its original one? The answer lies in the immense cultural and political influence of China throughout East Asian history.

For more than a millennium, the language of scholarship, government, and high culture in Korea was Classical Chinese. The Korean elite wrote in Chinese characters, known as Hanja in Korean, because a native Korean script (Hangeul) wasn’t invented until the 15th century and wasn’t widely adopted until the 20th.

Along with the writing system, Korea borrowed a massive amount of vocabulary from Chinese, covering everything from philosophy and science to administration. This huge influx of loanwords naturally included numbers. The Chinese number system was essential for record-keeping, currency, and calendrical science.

This created a linguistic division. The native Korean numbers continued to be used in everyday speech by all classes for simple, concrete counting—the way they always had been. Meanwhile, the borrowed Sino-Korean numbers became associated with written language, officialdom, and abstract concepts. The two systems settled into different roles, co-existing rather than one replacing the other. This division of labor has been passed down through generations and is still strictly observed today.

Dividing the Labor: When to Use Which System

The historical context explains the “why”, but for a speaker or learner, the “when” is most important. Here’s a practical guide to their modern-day roles.

When to Use Native Korean Numbers (Hana, Dul, Set…)

Think small-scale, physical, and countable.

• Counting physical things: This is the biggest use case. When you count people, animals, books, cups of coffee, or slices of pizza, you use native numbers. Crucially, you also use them with a specific “counter” word. For example:
  • 사람 세 명 (saram se myeong) — Three people (명 is the counter for people)
  • 맥주 두 병 (maekju du byeong) — Two bottles of beer (병 is the counter for bottles)
  • 고양이 한 마리 (goyangi han mari) — One cat (마리 is the counter for animals)

  Note: Notice how 1, 2, 3, and 4 change form (hana → han, dul → du, set → se, net → ne) when placed before a counter!

• Telling your age (casually): “저는 스물다섯 살이에요.” (Jeoneun seumul-daseot sal-ieyo.) — “I am 25 years old.”
• Hours on the clock: When you say what hour it is, you use the native system. “지금 세 시예요.” (Jigeum se si-yeyo.) — “It’s 3 o’clock now.”

A key limitation: The native Korean system is only used up to 99 (아흔아홉, aheun-ahop). For 100 and beyond, everyone switches to the Sino-Korean system.

When to Use Sino-Korean Numbers (Il, I, Sam…)

Think big, abstract, or systematic.

• Money and finance: “이거 오천 원이에요.” (Igeo ocheon won-ieyo.) — “This is 5,000 won.”
• Dates: Years, months, and days all use Sino-Korean numbers. “오늘은 이천이십사년 시월 이십오일입니다.” (Oneul-eun icheon-isipsanyeon siwol isib-oil-imnida.) — “Today is October 25th, 2024.”
• Phone numbers and addresses: Numbers are read digit by digit using the Sino-Korean system.
• Minutes and seconds: Here’s where it gets interesting! Minutes and seconds are paired with the native Korean hours.
• Any number 100 or higher: The words for 100 (백, baek), 1,000 (천, cheon), and 10,000 (만, man) are all Sino-Korean. So even if you’re counting 100 physical objects, you switch over.

The Perfect Mashup: Telling Time

Nothing illustrates the dual system better than telling time. It’s a perfect hybrid where both systems must work together in a single phrase.

To say the time, you combine Native Korean numbers for the hour with Sino-Korean numbers for the minutes.

Let’s say it’s 3:25 PM.

• The hour, 3 (세, se), is Native Korean.
• The minutes, 25 (이십오, isib-o), are Sino-Korean.

So you say: “세 시 이십오 분” (se si isib-o bun).

This beautiful mashup is a daily reminder of the two distinct historical streams that flowed together to create the modern Korean language.

More Than a Quirk, It’s a Cultural Fingerprint

While it might seem daunting, this dual system isn’t just there to challenge language learners. It’s a window into the soul of Korea. It tells a story of an ancient, native culture that held fast to its core identity while also masterfully absorbing and adapting powerful new influences.

Learning to navigate the two number systems is more than just memorizing rules; it’s learning to think in a way that’s deeply connected to Korean history. So the next time you order du cups of coffee for pal-cheon won, take a moment to appreciate the incredible journey those little numbers have taken to get to your lips.