Here are typical sizes for one and two-car carports:
12′ wide: 1 car
18′ wide: 1 1/2 cars
20′ wide: 2 compact cars but tight when opening doors
22′ wide: 2 cars
24′ wide: 2 cars with more space for opening doors with less risk of your doors hitting something
One way to calculate the right size for your carport is to park two of your vehicles beside each other and measure how wide you would need to comfortably open all of the doors on both vehicles.
A question many people ask is, “How much is a double carport.” Driving down the road you may recall seeing a sign on a carport that says double carport. Usually the metal carports with those signs on them are only 18×20 carports. Most people who want a double carport want to park two cars underneath. If you will be using your carport on a daily basis you will want a wider size.
If you only need enough space for one car and a motorcycle or a lawnmower, then an 18′-wide carport should work fine. But if you have a car plus a truck or an SUV, you’ll end up hitting your car doors on your other vehicles or on the steel carport tubing.
For two small, compact cars I would recommend at a carport that is at least 20×20. If you want a fully-enclosed carport with two garages doors, a 20×20 garage is the smallest garage that can fit two garage doors.
The next larger size double carport is the 22×20 which provides that little bit of extra room. The largest double carport is the 24×20 carport, which is great if you have two larger vehicles or just want extra room so you don’t have to worry about the door paint being chipped.