Photoshop Canvas Size Issue

[Timea35202475r03e]

Hello! 

I'm having some issues in setting canvas size to a certain value. I need a 240x120 mm document with 3 mm bleed on each side. In total I need the canvas to be set to 246x126mm. It just doesnt want to give me this exact value. I have checked for things outside canvas with Reveal All option, and checked if i have artboards which I think I dont have. I tried to set it first to 240x120mm and then adding 6 mm on width and height using Relative option. Still the closest i can get is 246.04x125.98 mm 

Do you have any ideas on this Issue. It would be a huge help since im sturggling with this for days already ... 

[Stephen Marsh]

Photoshop's native unit is pixels. 

What resolution is your document in PPi or PPCM?

[Timea35202475r03e]

PPi. Now I see that even If a create a new document with the specific measurements i need (without bleed) and check the measurements in Canvas Size the values are different?? How can this be? I tried resetting Essentials ( my preffered workspace) the result its the same 

[Timea35202475r03e]

Oh, I understand know what you meant with @davescm  's explanation. 

[Helen Cooper]

Check if there is a snap-to-grid feature. It might be adjusting the size slightly. If it is on, try turning it off.

[davescm]

To add to Stephen_A_Marsh's correct answer, because Photoshop works in whole pixels then the physical size will only be available to match whole pixels.

246mm x 126 mm at 300ppi would need 2905.51 pixels x 1488.19 pixels. But you cannot have a fraction of a pixel therefore it rounds to 2906 x 1488 pixels which, at 300ppi, is 246.04mm x 125.98mm.

Dave

[Timea35202475r03e]

Oh, I understand, so in order to have the exact value I need I should translate mm to pixels? 

[davescm]

You cannot have that exact physical size using 300ppi in a pixel image. A pixel image has to be in whole pixel units, not fractions of a pixel.

Dave

[Semaphoric]

You can, however, get the exact size by changing the resolution:

Yes, it says "point nine nine" instead of "point zero zero", but viewing with the width and height using  centimeters does give the expected value