I have made an image of a person and exported it with a certain pixel size. I then made another person that is a little bit smaller. Is there a way I can use the pixel size of the other object to figure out what pixel size to use for my smaller object?

Uuuhhmm....

Ok first, what do you mean by exporting with a certain pixel size? Do you mean you're drawing something of a certain pixel size, then exporting? Or do you mean you changed some options in the Export PNG dialog? If so, exactly what did you change? Or did you export (Save As) some other format? Exactly which options did you use?

I dont understand the export bit either but maybe this is what OP wants ?:

copy (CTRL + C) your first drawing (if its made of several objects it must probably easier if its grouped), then select your new drawing and go to Edit -> Paste Size (and use one of the options...'Height' probably...). That should make both drawings the same size.

Sorry for the confusion. What I meant was the export window. Basically, I drew a character for my game. I then exported it to a bitmap, and in the export bitmap dialog, I changed the export size to 64 by 64. I then noticed that when you go to export the same selection as a bitmap again, the size saves. Because of it saving, I was wondering if there was a way to set the scale. What I mean by that is this. Basically, I drew an accessory for the character beside it at a relative scale to the character. I would like to know if there is a function in inkscape where I can use that original export size as a sort of scale to make sure that when I export the accessory for the character (as a separate image), it stays at the same ratio of pixels.

Just use the same dpi value for both.

Like, exporting everything at a fixed dpi value?

Or exporting each object by the page area, moving the rest out of the page borders?

Yes everything at a fixed dpi value. But us there a way to extract the dpi from my originally extracted selection?

Nevermind, I figured it out. Thanks! Just didn't realise there was a dpi box...