Originally Posted by HankB
That's two racks of back ribs on one grate on my 18.5 WSM. It comes form the factory with two grates and a third is easily added to fit a total of 6 racks of back ribs. I think you can easily feed 10 on that.
Spare ribs take a little more space but I can fit six trimmed racks of those on as well. (I wind up firing my mini-WSM to handle the trimmings when I do six racks of spare ribs.)
You could probably fit 4-5 racks on each grate using a rib rack that holds them on their sides.