How these sizes are worked out
The US has no survey that measures rooms. The Census Bureau’s survey of new homes records the whole floor area — the median new single-family home finished in 2025 was 2,142 sq ft, the smallest since 2009 and 13% below its 2015 peak of 2,467 sq ft (Census Bureau) — and counts bedrooms and garage spaces, but never measures a room. Every room page here therefore sets four kinds of number side by side, and says which is which:
- Building code — the smallest a room may legally be. In the US that is the International Residential Code, which asks 70 sq ft of any habitable room except a kitchen (2021 IRC).
- Space standard — official minimums for new homes elsewhere, such as England’s national space standard and London’s design guidance.
- Survey — rooms as they are: US builders’ estimates of their typical new home (NAHB) and England’s housing survey, whose surveyors measure rooms with a tape (English Housing Survey).
- Worked out here — the space the things in a room need: a mattress and the clear floor round it, a parking space, a sofa at the right distance from a screen. These are computed from published sizes, and each room page shows the working.
Why the averages disagree
The builders’ figures are for new US homes and for the room where it exists as a separate room; the English ones are for houses of every age, measured as they stand. A main bedroom in a new US home averages 312 sq ft, where an English surveyor’s typical bedroom measures about 12–14 m² (129–151 sq ft). Neither is wrong — they answer different questions, which is why each room page lists both and says which is which.
Rooms and the whole house
Room sizes do not add up to a house’s size. The Census counts floor area to the outside of the walls and leaves out the garage and porch (Census Bureau); hallways, stairs and walls take the rest. The average house size page follows that number back to 1973 and shows how three different surveys measure it. To see what an area looks like as a whole, the size pages draw 500, 600 and 1,000 square feet to scale, and to measure your own rooms, the measuring guide and the calculator take it from there.