For example, if I set 40px for the title (in adobe XD design) how to convert it to the exact flutter font size
because I can't understand the flutter font-size property
40px in Adobe XD means 40px in Flutter. You can read the official document. Flutter font-size:
The size of glyphs (in logical pixels) to use when painting the text.
You can be confused about devicePixelRatio. You can find pt to px conversion from here.