'Sān jīn' literally means 'three catties' — a traditional Chinese unit of weight still widely used in markets and daily life. One jīn equals 500 grams (or half a kilogram), so sān jīn equals 1.5 kilograms. The character 三 (sān) is the numeral 'three', and 斤 (jīn) is the measure word for weight, historically derived from an ancient unit but standardized in modern usage. Unlike metric units like 'kilograms', jīn is deeply embedded in informal, spoken contexts — especially when buying food, produce, or meat.

This term appears almost exclusively in quantified noun phrases, typically following a classifier or directly modifying a noun (e.g., 三斤苹果). It rarely stands alone as a subject or object without context. While younger urban speakers may use 'kilo' or 'g', sān jīn remains essential for understanding street vendors, family cooking instructions, or regional dialects across China and Taiwan.