Why old units survive alongside the metric system
A unit that generations of people have used to picture a space, a weight, or a distance tends to stick around in everyday speech long after it disappears from official paperwork. Pyeong, don, and geun are simply easier to visualize for people who grew up hearing them, even when every contract and price tag is technically denominated in metric units.
Similar-sounding units exist elsewhere in East Asia too
Japan's tsubo, monme, and kan happen to match the Korean pyeong, don, and gwan almost exactly in size, since both countries adapted the same historical East Asian measuring system. China's traditional customary units share some of the same characters -- like li (ι) and jin (ζ€) -- but were standardized to different modern values, so the same character doesn't always mean the same amount across the region.
Frequently Asked Questions
Why is pyeong still so common in real estate?
Long habit is the main reason -- people have judged apartment sizes by pyeong for decades, so even though official contracts list the area in square meters, pyeong still comes up naturally in everyday conversation about housing.
Why does geun mean a different weight for meat and produce?
It comes down to differing traditional conventions: meat sellers settled on 600 g as one geun, while produce sellers calculate it as one-tenth of a gwan, or 375 g. If you want the exact weight, checking a scale directly is the safest way to be sure.