What size of motor is a Dodge Ram 1500 5.9?

The Dodge Ram 1500 with a 5.9L engine actually has a 5.9 Liter engine. That's the displacement, not the horsepower or torque rating, which varied slightly depending on the year and specific trim level. It's a significant engine size, however, meaning it's not expressed in terms of "size" in horsepower like a smaller engine might be (e.g., "a 100 horsepower engine").