Saving JPG in Photoshop with Proper Dimensions in Inches

[jacquieb24700998]

I'm saving large design files in photoshop as PSD, but when I save as a JPG, the size of the image seems to be way off (I place the file into Illustrator and it's way larger than I want it to be). How do I calculate the proper pixel size into inches so it's accurate? 

[D Fosse]

In a pixel based image file, physical size is determined by the pixels per inch number, ppi. You understand how that works when you repeat "pixels per inch".  That's a standard equation, as one goes up, the other goes down. Ppi is a measure of pixel density. When density goes down, say from 300 ppi to 72 ppi, size goes up.

A vector file works differently. It's not made of pixels, but mathematical formulae. So sizes are set directly and ppi no longer applies. Illustrator works directly with sizes.

Illustrator should read the size of the Photoshop file at the given ppi you have set there. If it doesn't, it's a bug.

What I suspect you have done here is use Export or Save For Web in Photoshop. Both will actually strip the ppi number because it's irrelevant for web/screen. Without a ppi number in the file, it will reopen with a default ppi number set. With Adobe applications, that default number is 72.

[jacquieb24700998]

Thank you for your response. I think you're right about it being a bug because it worked a couple times for me, now it's a major issue.

[gener7 · Accepted solution]

As I understand it, File > Save a Copy > Jpeg will preserve the ppi metadata. Use that instead of Export.

I could have said "Save As", but it's a legacy behavior that has to be set up in Preferences > File Handling > File Saving Options.

[jacquieb24700998]

Oh my goodness, this worked! I've been pulling out my hair for two days trying to figure this out. Screen shot this! Thank you so much.