The mathematics should not require the IQ of a genius.

A row in a font bitmap contains either 11, or 32 characters. Thus, when the width is divisible by 11, then the character width is 1/11 the bitmap width. Otherwise it's 1/32 the bitmap width.

In the first case the character height is the same as the bitmap height, in the second case it's 1/4 or 1/8 the bitmap height, dependent on whether the bitmap width is more than 4 times its height, or not.