How big is 400 square feet?
By Rohit GaurLast updated October 30, 2026Report a mistake
400 square feet (37.2 m²) is a 20 × 20 ft space, or 16 × 25 ft laid out longer.
400 square feet is twenty feet square, and that is not a coincidence in a suburb: Mill Valley, California, defines a two-car garage as at least 20 × 20 ft measured to the outside of the building (City of Mill Valley). Many garages you have parked in are exactly this.
As a home it is a studio or a small one-bedroom apartment — smaller than the American average for an apartment, which the federal energy survey puts at 918 sq ft in buildings of five or more units and 887 sq ft in buildings of two to four (EIA).
Twenty by twenty is the square layout; 16 × 25 gives a longer room that takes a kitchen along one wall. Either way, everything in a 400 square foot home has to do two jobs. The garage sizes page shows what fits in the parked-car version of this space.