Most doll houses are 1:12 scale compared to real life.
It seems like a strange conversion, why not something more even, like 1:10, for example?
But it really makes a lot of sense, in the non-metric United States, anyway.
There are 12 inches in a foot, so if you want to scale something in our world down to doll house size, first determine its size in feet, then turn that number into inches.
A 6 foot person here becomes a 6 inch doll.
A 30 foot room becomes a 30 inch room. Simple.