Problem with outline width

[cassiopoia]

Hi all, 

I am doing a project where I am designing some new pieces and also working with existing pieces that were designed by someone else. I have png files from the other designer, and then I have my own designs. I need to add a white 5mm outline to all the pieces. When I add the outline by typing "5mm" into the radius option on the effects tab, the outlines turn out to be different sizes for the pieces they designed versus the ones I designed, even though the relative sizes of the objects are the same (around 2500 pixels in width). My outlines end up being 14.2 pixels, and the ones on the other designs are 59.1 pixels. 

I'm fairly new to this program and have no formal education in design, so maybe this is a simple thing that I'm not understanding, but please help! 

[walt.farrell]

Sounds like one document  is 72dpi and the other is 300dpi. 

[cassiopoia]

Ahh thank you very much, that fixed it! 

[walt.farrell]

You're welcome