Inch to mm

[Pistill]

I need to deliver a file in the exact measurement of 227x285mm and in 300dpi.

So far I have been working in 300ppi (thats what photoshop offers) which I understand is the same as 300dpi. No matter how I try the file when going from pixels to mm comes out to 226.99x284.99mm. This might not seem like much but the uploader for the artowk wont accept unless the measurement is exact. What am I doing wrong?

[c.pfaffenbichler]

A digital image per se has no dpi but ppi – dpi and ppi are not the same. 

dpi applies to output devices like plate-setters. 

What are the image’s pixel dimensions? 

What file format do you provide? 

[D Fosse]

It's inches vs. millimeters. That specification is in fact impossible if exact numbers are required. It can't be done with clean numbers and someone should tell them so because I can't imagine it matters in practice.

Pixels per inch doesn't give you a round number in millimeters, unless the numbers are big enough. They aren't here.

If it's a matter of getting this uploaded or not, I'd just increase size or ppi until it's accepted by this dumb uploader.

[c.pfaffenbichler]

300ppi corresponds to 118.11pcm so, as D_Fosse pointed out, the intended size-lengths in mm do not correspond to integers. 

[Pistill]

Yes I figured it was the pixel that can't be even to the cm...

So when I play around with setting up a new file I can get the mm dim even if I use the other drop down option ppcm instead of ppi. But now this messes up the quality of the file. Do you have any experience here? Essentially leaving the file to 118.1 and save will generate a less quality for me. I can see this also in the file size that dropped from 33MB to 1.6MB.

[D Fosse]

300 pixels per inch = 118.11 pixels per centimeter. Again, rounded numbers but otherwise the same.

Changing units, or even changing the number, doesn't change anything in the file, as long as you don't resample. If you get a smaller file size you have resampled. Do it again without resampling.

[Lumigraphics]

Tell them its not possible. One of those numbers has to change.