Well, technically 18 cubic feet is the limit... but you get the point, right? My car already looks like a box, so I decided to put another box on top. It holds everything I have ever needed it to. 5-6 Snowboards and boots in the winter, way more camping gear than you'd ever need in the summer and since my Honda Element only has 4 seats on the interior, this bad boy can be used to put an extra passenger in. I don't think Yakima would support this statement, but they sure did make enough room for it! Getcha' some!