Square footage of Prius cargo area with seat down.

Google it

 

With my front seats on my V where a 6' person might have em, I measured 68" by 40". The 40" is between the wheel wells and not the widest point. The 68" is at floor/rear-seat-down level to just short of my front seats but it might be shorter the higher you go by a few inches. And the 68" is beyond the seatback and over the headrest but not touching the seat back. I'll leave the math to the observer.

The problem with answering this question is that it isn't a nice rectangle that stays constant.

The rear seat moves forward and back and the front seats move forward and back. Either or both could change the dimensions. Likewise the rear seat backs fold down (very easily) and are maybe an inch and a half higher then the rear cargo compartment. But they have hard backs so cargo can rest on them just fine. And there are two seat back sections of the back seats so the dimensions change if you have one down or two down. Both front and back seats recline so the seat back angles could change things. And the rear hatch is angled too. And the rear wheel wells intrude. It isn't a flat sided mini-van with a perfectly flat floor and a flat tailgate and it doesn't get MPG like one.

If these aren't the dimensions you want, ask the question again. Or visit a dealer and measure the dimensions you are interested in. I can't imagine a dealer not letting you.

 

Max I've had in mine was a 6' Xmas tree or, on a trip to COSTCO, I go with 5 large Styrofoam coolers and bring back those and several large boxes of goodies and some sacks of wine from Trader Joe's. When you look at my mileage (on regular gas) keep in mind I bought in November so the heater has been on the whole time I've owned it which costs and I drive it pretty much as a normal car, no tricks to try and increase mileage.