In picking my flours, I confess, I just hope to guess right. This subject really frustrates me, it's like the lack of proper measurement (=use of scale for ingredients) in the North American world.
A lot of my professional european recipe call for the W (strength) of the flour.
More or less, I need to look at the protein % to guess the W.
Weak less then 180 W (8-9% protein)
Meadium betwen 180-280 W (10-11%)
Strong Higher than 280 W up to 400 (more then 11%)
A lot of flours don't really carry the protein content as I percentage, but I guess it's a simple calculation a serving size 30 g with a protein amount of 3g must be a 10% protein.
Do you pay attention to this? Are there specific mills/flour brands that you like to use targeted to more professional approach to baking?