ROI calculation

So you're trying to figure out based on space in a catalogue how much ROI you get for a product, if the product takes up 0.035 space on a page, and the page is 1 of 72 in a catalogue? I would think the traditional way to calculate ROI would be based on how much the (your example) the toy cost you (your costs) plus overhead (shipping, handling, labor, taxes, building, electricity etc) then how much you sold it for.

So do you have an Excel spreadsheet that details all of these toys, money generated, page space etc?

Alright, using your example, if you have £31,000 for 50,000 catalogues, the price per copy is £0.62, if your catalogue is 72 pages, the price per page is £0.01 and if the space on one page taken up by a toy is (toy 1 in this instance) 0.035, assuming all else is equal, then your price for toy 1 on the page is £0.00030 (72/£0.62)*0.035 and I would probably distribute that cost over the 50,000 copies and that would equal £15.07 for your "costs" for toy 1. Now if the sales generates £1,793.00 AND you have no additional costs, you're just acting as a middleman, you don't buy it, you don't stock it, you don't have any holding or transfer costs, then I would think your ROI would be your (£1793-£15.07)/£15.07 or about 118 ROI. I'll be interested in seeing how others answer this.