I have this expression:
12 × 3 mm².
I guess that it should not be pronounced as "twelve multiplied by three millimeters squared". I've tried to google it already but it seemed to be difficult because of my lack of proficiency in searching keywords.
Note that 12 x 3 should be pronounced in the same way as shape e.g. 4x2 rectangle (rectangle with width = 4 and height = 2).