A fullsize car rental (often also know as standard size) will have either 2 or 4 doors... 4 door fullsize cars are the most common, but usually not guaranteed.
Some examples of common makes and models are
The seating capacity of a full size car is usually 5 passengers... 2 seat belts in front, 3 in back.
Average Luggage Capacity
The average luggage capacity given for a fullsize rental car is
2 Large 2 Medium 2 Small -- pieces of luggage
I usually find the luggage capacity information provided by rental car companies to be very conservative... depending on what type of luggage items you have, you can probably fit more. If you have concerns about the luggage capacity of a full-size rental car, visit a car dealership and ask to look at the trunk of such a vehicle.
Some common standard features that you will find in a fullsize rental car are
Power Brakes, Power Steering, Power Windows, Power Locks
Tilt Steering Wheel
Average Fuel Economy
The average gas mileage on such a car is
19 mpg – city
27 mpg – highway
If you see two options for seating capacity on a full size car, it means that the car rental company has both options in that category. You are guaranteed 5 passenger seating. Whether or not you get 6 passenger seating would depend on what make/model you get at the rental counter. Makes and models are rarely guaranteed...usually only in a specialty car class.
Note: In general categories, companies can rarely guarantee a make or model. That’s why you’ll usually see a make/model example with a notation of …or similar. That means you will get either that vehicle or something of similar size and with similar features.
A fullsize rental car will usually be the most economic option for 5 passengers. A luxury or premium car will be larger and more comfortable, a minivan or SUV even more so -- but the price difference (and possible mileage restrictions) usually make the full size car a more price-wise choice.