寝室（しんしつ） is the standard word for bedroom, especially in writing, floor plans, and real estate listings.
In casual conversation, people may say ベッドルーム or simply 部屋（へや） instead, depending on the context. 寝室 can sound a little more formal or practical, like “the room used for sleeping.”
寝室 describes the room’s function, not its style. It can be a Western-style 洋室（ようしつ） or a tatami 和室（わしつ）.
In housing layouts, 寝室 may refer to the main bedroom. Smaller rooms may be labeled by type, such as 洋室（ようしつ） or 和室（わしつ）, rather than as bedrooms.