Korean Units & Numbers for Foreigners: Pyeong, Age, Sizes, Distance & More

Korea runs on a few number systems that quietly trip up every newcomer: apartment sizes in pyeong, your age that jumps by one or two overnight, clothing sizes that don't match anything back home, and distances in ri. None of it is hard once someone explains it — so here is the whole thing in one place, with a free calculator for each.

1. Pyeong (평) — how apartment sizes work

Every Korean real-estate listing shows area in both m² and pyeong (평), a traditional unit. The exact ratio is 1 pyeong = 3.30579 m² (not the "3.3" you'll see quoted), so an 84 m² flat is about 25.4 pyeong. The bigger trap is that listings mix two different areas: supply area (what you pay for, including shared space) and exclusive area (what you actually live in). An "84 m²" apartment usually means 84 m² of exclusive area, with a larger supply area.

Convert any number with the square-meters-to-pyeong converter, and decode the exclusive-vs-supply trap with the apartment area & price-per-pyeong tool. For the full story, see "Korean Pyeong, Explained."

2. Korean age — the two systems (and the 2023 change)

You may have heard that Koreans are "one or two years older." Until 2023, three age systems coexisted: Korean age (born at 1, +1 every New Year), international age (0 at birth), and calendar-year age (current year − birth year). Since June 2023, international age is the legal and administrative standard — but "Korean age" still shows up in casual conversation, so it helps to know both.

See all three at once with the Korean age calculator. And if you have kids, Korean school grade is set by birth year, not age — check it with the Korean school grade calculator.

3. Clothing & shoe sizes

Korean shoes are labelled in millimeters: a US men's 9 is about 270 mm, a US women's 7 about 240 mm. Tops and dresses often use a numeric system (85, 90, 95, 100…) that roughly maps to XS–XL, and women's sizes sometimes use 44/55/66/77. It's close to but not the same as US/EU sizing, so always convert before you order online.

Convert US/EU ↔ Korea with the clothing & shoe size converter.

4. Distance — ri (리), miles, and km

Korea uses kilometers for everything modern, but you'll still meet the traditional ri (리) in idioms, place names, and old texts — and if you're arriving from the US, you'll want to convert miles too. 1 ri ≈ 0.393 km, so the famous "삼천리 (three-thousand ri)" describing the length of the Korean peninsula is about 1,200 km.

Convert ri / miles ↔ km with the distance converter, and °F ↔ °C with the temperature converter (Korea is Celsius-only, so 38 °C is a heat-wave day, not a fever).

5. The business registration number (사업자등록번호)

Doing business, freelancing, or signing a lease? You'll see 10-digit business registration numbers everywhere. They carry a built-in checksum (the 1-3-7-1-3-7-1-3-5 weighted algorithm), so a single tool can tell you instantly whether a number is even structurally valid — a quick sanity check before you wire money.

Validate any number with the business registration number validator, and see how the checksum works in "What the Checksum Tells You."

6. A few more you'll hit

Names: romanize your Korean name for a passport or card with the name romanizer. Money: Koreans count in 만 (10,000) and 억 (100,000,000), so "3천만원" is 30 million won — our calculators show the 만/억 reading next to big amounts. For the full arrival-to-departure picture, read the complete guide to living in Korea.

All tools are free, need no sign-up, and work on mobile. Bookmark the ones you'll reuse — the ㎡↔pyeong and age converters come up more often than you'd think.