A typical large family car like the Ford Mondeo is about 15 by 6 feet (4.6 m × 1.8 m), meaning that even with the larger size garage, it is necessary to park to one side to be able to open the driver's door wide enough to enter or exit the vehicle.
https://en.wikipedia.org/wiki/Garage_%28residential%29
A lot of times if someone is wanting to get a double carport they want to park two cars underneath the carport and for most people especially if it is going to be used on a daily basis you will want to go with a slightly wider size.
http://www.alansfactoryoutlet.com/blog/bid/87170/Double-Carport-Size-Style-and-Prices
In some places, the term is used synonymously with  carport , though that term normally describes a structure that, while roofed, is not completely enclosed. A carport protects the vehicle to some degree from inclement weather, but it does not protect the vehicle from theft or vandalism.
https://en.wikipedia.org/wiki/Garage_%28residential%29
Carport plans are shelters typically designed to protect one or two cars from the elements. They are also used to protect other large, bulky or motorized items that might not fit in a garage or basement. Most carports are open-sided on at least one or two sides, if not all four sides.
https://www.thegarageplanshop.com/carport-plans/garage-plans/78/1.php
Typically, a small British single garage is 8 by 16 feet (2.4 m × 4.9 m), a medium single garage is 9 by 18 feet (2.7 m × 5.5 m), and a large single garage is 10 by 20 feet (3.0 m × 6.1 m).
https://en.wikipedia.org/wiki/Garage_%28residential%29
Residential garages typically have space for one or two cars, although three-car garages are used. When a garage is attached to a house, the garage typically has an entry door into the house. Garages normally have a wide door which can be raised to permit the entry and exit of a vehicle, and then closed to secure the vehicle.
https://en.wikipedia.org/wiki/Garage_%28residential%29
Another option is to get a double carport and enclose a shed area in the back end for enclosed storage like shown in this picture. As you can see the metal carports can be used to store a variety of items besides a car or truck. Here is a list of the metal carport sizes and prices. Once you decide on the size you will want to figure out which style carport you want.
http://www.alansfactoryoutlet.com/blog/bid/87170/Double-Carport-Size-Style-and-Prices
If you would simply prefer to talk to someone about the correct sized carport for your needs, give us a toll-free call at (855) CAR-PORT and someone will be happy to assist you with pricing.
http://www.carport.com/metal-carports/standard-two-car-double-carport/
A question many people ask is how much is the double carport. Driving down the road you may recall seeing a sign on a carport that says double carport. Usually the size of the steel carport kits for sale with those signs on them is a 18x21 size carport.
http://www.alansfactoryoutlet.com/blog/bid/87170/Double-Carport-Size-Style-and-Prices
The purpose of a carport plan is similar to that of a garage. They are intended to protect cars and other vehicles, such as a boat, camper, or Jet Ski, from wind, rain, sun, snow and ice. Carport plans range in size and style ensuring you’ll find the right one to satisfy your needs and fit your lot. Some 1-Car garage plans, Garage Plans with Carports and Drive-Thru garages are similar to carport plans in different ways. Carport plans are popular choices when it comes to sheltering vehicles because they are a less expensive alternative other residential parking options such as detached garage plans. They are sometimes referred to as sheltered parking and outdoor covers.
https://www.thegarageplanshop.com/carport-plans/garage-plans/78/1.php
how wide is a two car carport
The two car carport is 18x21 wide.