A 36" (90 cm) dish is the recommended size for the majority of signals for KU band in North America. Some people go with a larger dish if they are located on the fringe of a satellite footprint or want better signal reliability in adverse conditions.
Dishes up to 39" / 1 meter are protected by FCC regulation for installation in HOAs, apartments, etc. Larger dish installs are subject to rules and regulations set by the HOA, city, property management.