For text fonts, 1 pt = 1/72 inches. So, if you set the font size of the text to, say, 36 pt., the character height will be 1/2 inch or 1.27 cm. I suggest you do some actual measurements to verify and work with those measurements. MATLAB's "extent" property for text includes margins, so I'd be hesitant to use those width and height values.
As for visual angle, that's an arctan calculation. You need the size of the characters and the distance of the participant's eye from the display. For example, the visual angle in degrees for a character 1 cm in size viewed from a distance of 65 cm is