Hi flexi, and welcome! I see you posted a duplicate of this post in the German forum. Because both the English and German language forums are quite active, so you don't need to do that.
As chrisb wrote, post your file and your FreeCAD info if you want better answers. I can offer a little help now though.
flexi wrote: ↑
Thu Aug 22, 2019 12:41 pm
I can set the arrow size to 20mm and the font size to 100mm to see the values but I am sure there is a easier way to do it?
Change to the Draft WB or Arch WB and from the pull-down menu choose Edit > Preferences > Draft (icon in left pane) > Texts and Dimensions (tab in right pane) and change the settings to your liking. You might have to quite FreeCAD and re-start it for the changed Preferences to take effect. But because you want to make a 2D drawing of your 3D model in TechDraw, using Draft WB > Dimensions is probably the wrong approach. So, here is where having the model and your proper FreeCAD info will help us get you going in the right direction without a bunch of false starts.