일 to 십 — Sino-Korean for everything except things and ages
The second number system in Korean is borrowed from Chinese: 일 (1), 이 (2), 삼 (3), 사 (4), 오 (5), 육 (6), 칠 (7), 팔 (8), 구 (9), 십 (10), 백 (100), 천 (1,000), 만 (10,000). You'll use Sino-Korean for phone numbers, money, dates, room and bus numbers, minutes, addresses — anything that's a label or a quantity that can get big. Native numbers (lesson 5) are for counting tangible things and giving age. Telling time uses BOTH at once.
The first ten
일 (1), 이 (2), 삼 (3), 사 (4), 오 (5), 육 (6), 칠 (7), 팔 (8), 구 (9), 십 (10). They're all one syllable. Korean kids learn them as a chant just like the native numbers. Above 10, you build numbers compositionally: 십일 (11 = 10+1), 십이 (12), 이십 (20 = 2×10), 이십삼 (23 = 20+3), 백 (100), 이백 (200), 천 (1,000), 만 (10,000).
Phone numbers and money
Phone numbers are read digit by digit using Sino-Korean: 공일공 (010) — note that 공 (zero, literally 'empty') is more common than 영 for phones. Money: 천 원 (1,000 won), 만 원 (10,000 won), 십만 원 (100,000 won). Korean groups numbers in 만 (10,000), not 1,000 like English. So 100,000 is 십만 (10 × 10,000), not 'one hundred thousand'.
Dates: 월 (month) and 일 (day)
Months are Sino-Korean number + 월: 일월 (January), 이월 (February), 삼월 (March)… 시월 (October — note 십월 → 시월), 십이월 (December). Days are Sino-Korean number + 일: 일일 (the 1st), 이십오일 (the 25th). Years are Sino-Korean too: 이천이십육년 (2026).
Time: hours native, minutes Sino-Korean
This is the one place the two systems sit side by side. The hour uses the native count + 시 (lesson 5): 두 시 (2:00). The minutes use Sino-Korean + 분 (minute): 이십 분 (20 minutes). So 2:20 is 두 시 이십 분. 'It's 3:45' = 세 시 사십오 분이에요. Memorize the split: clock-hour native, minute Sino-Korean.
Native vs Sino-Korean — when each shows up
Native (lesson 5): things, people, animals, ages, hours of the clock. Sino-Korean (this lesson): phone numbers, money, dates, minutes, room/floor/bus numbers, math. Quick test: am I labeling something or telling math? → Sino-Korean. Am I counting things you can hold? → native. There are exceptions, but this rule covers >90% of cases at A1.
