Ah! now I see what you're asking. Each size tub is going to have different dimensions. My 41qt tub is 6" tall. My 32qt tub is 6-1/4" tall and my 15qt tub is 6-5/8" tall so if you space all of your shelves equally then some tubs will need lids and some won't. The other option is to figure out how many tubs you want of each size and then build the rack to fit them...