According to the DIY Network a 3 car garage is about 950 sq. ft.
It would depend on the size of the one car garage and garage door opening.It depends on the size of the garage. Not all one car garages are the same size.
What is average size of two car garage?
Sixty feet is a good size width for a 3 car garage. This comes from the Illustrated Guide to Tactical Drawing: How to Determine Floorplans. It calculates the size of the cars with doors open and adequate space to walk between vehicles.
A two car garage is usally 24 feet X 24 Feet.
Certainly - however, sometims the 3rd space can only accomodate a golf cart, none the less, it is still a car space and counts as 3 car garage.
16 by 7
It varies on what size car you plan on putting in it.
10' x 20'
The standard width of a double car garage is 20.5 feet. That is a big enough size to fit a large sedan and a truck inside.
Most are mot big enough and most are around 24x22. A much better size for a 2 car garage is 30x28.
The average two car garage measures 24 feet by 24 feet. Some are larger, but very few would be much smaller.