Based on my many years all manufactures of all Travel Traiers quote the overall length of the entire travel trailer from the tip of the tounge to the back end of the unit. The actual useable space inside the unit is about 3 feet shorter...this deduction in what I call "people space" does vary by a few inches from manufacturer to manufacturer...bring your tape measure.
Another factor to consider is the actual width of the unit...this can be from about 7 feet wide to about 8 feet wide. Actual useable space and the use of that space often determines how happy you will be when you camp in the unit. Layouts are important. When you shop for a Travel Trailer try to visualize you and your family adjusting to life in the unit. If the layout and size does not work you will not be a happy camper. That is the reason there are so many lightly used units for sale
Unhappy campers often sell a unit in the first year after failing to adapt to cramped and poorly designed layouts.