The Keret House, a proposed single-occupancy office and residence in Warsaw, Poland, will be built between two existing buildings and feature an interior width of only 72 centimeters (28.3 inches) at its narrowest point.

Related Fact: The home recently completed by Indian billionaire Mukesh Ambani could fit 2,535 Keret Houses inside of it. At 27 stories and 398,000 square-feet, it is the world’s largest home.

[Sources: Arch Daily and Inhabitat. See previous Numbers of the Day here. ]