The standard NYC lot is 20x100 (some a little bigger, some a little smaller). The prewar walkup rowhouses that blanket the city fill the lot basically entirely, and can easily fit 20 units (one-bedrooms or studios) in dense/expensive areas. I lived in one up until recently -- 5 stories, 4 one-bedroom apartments per floor. The rowhouse schema is very flexible: in outer boroughs they can be single family, while in Manhattan they are endlessly subdivided. For examples of the type see:

https://urbanomnibus.net/2016/04/201604typecast-the-row-hous...