The murti of Hindu God that should be worshipped in home should be of small size. The general rule that is followed is that the height of the murti should not be of more than 22 cm. This rule is generally followed when murtis of Ganesh, Vishnu, Lakshmi, Krishna , Saraswati and Shivling is placed in puja rooms. The rule is strictly followed by Hindu homes in North India .
But when murtis of Ganesha, Saraswathi, Vishwakarma etc are used during pujas like Saraswati Puja, Ganesh Chaturthi Puja the size can be more than 22 cm. But it is always better to use small murtis even for temporary pujas.
Huge murtis are worshipped only in temples or in sacred places.