I've never fooled with the DPI setting—I'm not sure I even realized Excel has one—but it makes sense to me that if you change that, then your worksheets (etc) won't fit the margins in the same way. The margins are measured in inches or centimeters, so once you tell Excel to use more or fewer dots per inch, naturally the printed documents will be smaller or larger, respectively, and no longer fit the same into the printed margins.

If what you're asking for is some solution that will cause your documents to print at the same size at each user's station no matter what DPI setting those users have, it isn't obvious to me that there can or should be one. That's what DPI is.

Hm; is the DPI setting by workbook? If so, at least it'll get to your users set correctly, and if they change the DPI setting on your workbook after they've received it, they have only themselves to blame for the results. But if there's a single DPI setting covering the whole Excel application, it isn't clear to me what you can do. Maybe choose the lowest DPI setting that you think is likely to be on any other workstation—the fewest dots/inch likely, ie the largest dots—then set the margins etc to fit that. On other machines your pages will appear smaller, then, but they won't lap over onto other pages. But it's kludgy.

Why would you think other users would fool with DPI in Excel anyway?

...I wrote all the above, then reread your post and decided you probably aren't talking about a DPI setting in Excel. On your screen, maybe? That wouldn't change what fits in printed Excel margins, though. On your printer? Where?