Toyota's site lets me know how many golf balls I can fit in the cargo area but I am carrying larger goods and need to know the *linear* dimensions of the cargo area, including the width between wheel wells, preferably in inches but I don't mind converting metric. This is such a basic datum, I don't understand why car makers don't include it. The volume measurements are OK for comparing with competition but, as an ordinary consumer, I find linear dimensions more meaningful.
You could try Edmunds.com. They have reviews and specs on cars. It may have the info you are looking for...
Buy a tape measure and visit a dealer.
I own a tape measure. I could visit all the dealers and collect linear dimensions for every model I'm interested in, then tabulate and publish the data for others seeking similar information. When I have the leisure to do so, I'll probably find something better to do.