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Millimetres to Pixels

Hi Guys

I am converting mm to pixels using Indesign and Photoshop which both produce the same result, 12mm to 34px.

If I use an onLine converter I get a totally different result, 12mm to 45.4px.

Can anyone explain why and what is best to tell a client to go by for their Brand Guidelines?


Paul Murray

Staff member
I just specify in physical units such as mm or pts, since pixels are screen measurements and technically don't exist in physical space. Add into the mix retina devices where elements can be twice or three times as big and you've got a lot of confusion.
If you're looking to convert mm to pixels for an image to be printed at 300dpi then you can multiply by 11.811.

For example if you want to print an image that is 120mm across then it needs to be 1417 pixels across.

This information is from The Print Handbook.