I am recreating the symbology of a cartography moving from ArcMAP to QGIS substituting some font symbols in arcmap and reproducing them with new .svg symbols. The problem is that setting the size of symbols according to ArcMAP (points, millimeters) in QGIS the dimensions of the same symbols at the same displaying scale are very different (larger). The definition (and printing) scale is 1: 10,000 and map unit is meter. I'm confused about a way on how to match the same scale of symbols between ArcMAP and QGIS. Update:
In ArcMap, if you have the option 'Scale symbols when a reference scale is set' activated in the Display options of the layer's Properties (default), it will influence the symbol size. If that option is deactivated, the symbol will have always the same size regardless of the current scale of the map.
In ArcMap, the relation between the size in mm and in points seems to be: 1 mm ≈ 2.83464 pt (regardless of the reference scale).
You should think of the size in mm as the size you want the symbol to have in a printed page at the reference scale.
In QGIS, if you have your map units in meters, the size of the symbol that you set in the style definition is the size in mm that the symbol would have in a printed page a the scale of 1:1.000.
For instance, if you have a square Simple marker with a size of 5 and the unit is set to Map unit, when you print the map at the scale of 1:1.000, the symbol will have 5 mm in the page. If you print the same map at the scale of 1:500, the symbol will have 10 mm in the page.
In QGIS, setting the symbol size in Map units, it would be as if, in ArcMap, you were setting the symbol size in mm on a map with a reference scale set to 1:1.000.
Since, for what I understand, you are changing from a map with a reference scale of 1:6.000 in ArcMap to a map that you want to print at a scale of 1:10.000 in QGIS, you should change the size of the symbol (in mm) in ArcMap by a factor of 0.6 to set the size of the same symbol in QGIS (unit set to Map unit).
For instance, a symbol with a size of 2 mm in your ArcMap project (reference scale of 1:6.000), would be set to a size fo 1.2 Map units in QGIS.