Is 16x20 feet big enough for a 2 car garage?
The ideal size will vary with the size of the vehicles you drive. There is a vast difference in the space required to comfortably open the doors and exit a Mini Cooper and a full size pick-up. I live in an older home with a 2 car garage built in the 1920's. The inside dimensions are 18' by 18'. To fit 2 cars (06 and 08 Chevrolet Impala) in it, the one on the left must be backed in and the one on the right driven in. Exiting the vehicle requires caution to keep the doors from dinging each other. Opening the passenger doors is impossible as there is less than a foot of clearance to the wall. Doing any kind of repair or maintenance in the garage is impossible with both cars inside.