The carrying capacity of a 2007 Ford Ranger depends heavily on the specific configuration (cab size, engine, drivetrain, and options). There isn't one single number. You need to look at the sticker on the driver's side doorjamb or your owner's manual. This sticker will list the Payload Capacity (which is the carrying capacity).
The payload is the maximum weight of passengers, cargo, and any added equipment that can be safely carried in addition to the vehicle's weight.