层

层 (céng) is primarily a measure word meaning 'floor / story' (of a building) or 'layer' (of anything stacked). Use it to count floors — 三层楼 (a three-story building), 我住在五层 (I live on the fifth floor) — and to count layers — 一层雪 (a layer of snow), 三层蛋糕 (a three-tier cake). Two important differences from English: first, in Mainland Mandarin floor numbering is identical to American style — 一层 = first floor (ground floor), 二层 = second floor, etc.

— unlike British English where 'first floor' is one above ground; second, 层 and 楼 (lóu) are often interchangeable for floors (五楼 and 五层 both mean 'fifth floor'), with 楼 more spoken and 层 slightly more written / official. Beyond buildings,