Millimetres to pixels

[emilesilvis]

Hello everyone.

In Affinity Designer, when I select the A3 preset in Document Setup, I see the dimensions in millimetres as 297mm x 420mm.

When I then change the Document Units to pixels, I see the dimensions in pixels as 3507.9px x 4960.6px.

When I do the same thing in Inkscape, I see the dimensions in millimetres are the same, but the dimensions in pixels are 1122px x 1587px. When I put the same millimetres numbers into https://www.unitconverters.net/typography/millimeter-to-pixel-x.htm, I also get 1122px x 1587px.

Is this expected behaviour?

Thanks.

Edited May 22, 2020 by emilesilvis
Specify Affinity Designer

[John Rostron]

The conversion from millimetres to pixels will depend on the document resolution (dpi or ppi). For  vector program such as Designer, this does not really have any meaning until you wish to print the document or export to a raster format (such as png). Different programs will make different assumptions about the resolution, hence the different dimensions.

John

[emilesilvis]

Hi John. Thank you for the explanation! I learned something new today.

I looks like both Inkscape and https://www.unitconverters.net/typography/millimeter-to-pixel-x.htm assumes 96 DPI. 

[walt.farrell]

It looks like the document in Designer is at 300dpi, but the document in Inkscape is at 96dpi.

[Andy05]

9 minutes ago, John Rostron said:

For  vector program such as Designer, this does not really have any meaning until you wish to print the document or export to a raster format (such as png).

Well, unless you use high-res (contradiction here already!) "vector" brushes in your illustrations. Size vs. resolution is irrelevant to true vector graphics. Unfortunately, I't not relevant to AD at all, as some "vector" tools are pixel based, not true vectors..