I also believe the cargo dimensions quoted for the mazda5 are wrong... In the canadiandriver.com review of the mazda5, the cargo volume listed (3rd row folded) is :
Cargo capacity 1256 litres (44.3 litres)(3rd seat folded).
( see canadiandriver Test Drive: 2006 Mazda5 GT )
That was consistent with the specs from mazda.ca back then... perhaps the specs on mazda.ca are wrong now???
Would be nice to get the facts right on this one...
Figures for one car or the other are definitely wrong. According to the review here, the Kia is 65mm wider than the Mazda but 65mm shorter. That means that the surface areas of the two vehicles are identical. Since the Kia is only 20mm taller, that means short of leaving the engine out, there is no way that the Kia could have twice as much rear space behind the second row of seats than the Mazda5.
In any case, I know from personal experience. I was on a consumer panel this summer and had the opportunity to drive a Kia Rondo for a month. They had recruited Mazda5 owners to get comparative impressions. It always felt to me like the Kia's cargo room was smaller. Faced with a week's trip with three people, luggage, and a Newfoundland dog, I needed all the space I could get. Since I felt obliged to drive the Kia, I decided to measure the space behind the second row of seats in both the Kia and the Mazda 5. I found that the Kia was wider, but the Mazda was longer. Tthe cargo areas were identical in size.
I finally took the Mazda on the trip. Neither car could hold everything and I had a roof rack for the Mazda. Kia had not yet developed a rack for the Kia, so I had no choice.
I will say this, though -- both cars have far more interior room than any of their purported competitors -- the Chevrolet HHR, the PT Cruiser, or the Toyota Matrix. I haven't driven the Matrix so I won't comment, but I would easily choose either the Mazda5 or the Kia over the HHR or the PT Cruiser. You get far more car for the money with either one.