I will be travelling to Scandinavia in mid-July for a few weeks. We have some city sight-seeing (Stockholm, Copenhagen) as well as time on the fjords in Norway. I've been keeping a watchful eye on the weather forecasts and plan to adjust my packing on the last day based on the temperatures. However, I wanted to be ready with a rough guideline so that I can quickly pack more or less of something.
Leaving aside the fjords as gear can be easier to pack, here is a rough draft of the translation temperature / clothing for city sightseeing:

18 degrees & below - long trousers + closed shoes
19 - 23 degrees - cropped trousers + closed shoes
24 - 27 degrees - cropped trousers + sandals
28 degrees & above - skirt/dress + sandals

I am only including the bottom parts as they tend to be a lot harder to adjust on the fly (can't take off my trousers if a bit too warm), whereas with top layers I always start with a short-sleeve top, then add a cardigan, then a jacket, etc. and take off as I go along.

Please give me feedback, especially those living in Europe or who have recently travelled there: does this hold water? The temperature in Scandinavia seems to be around 20-22 maximum each day: what are you wearing?

As a final remark: I tend to run warm and being too hot makes me feel miserable. My experience is that I most often pack too warm for Europe and end up sweltering.