How to set font font settins

[Dimyas313]

How to I get the correct font metric for font design size of 24. Also, my view box is also 24x24
Is there a simple calculator on line that can help with this for the math challenged like me?

# Size (in pica points) for which your font is designed.
font_design_size: 24

# The em size. Setting this will scale the entire font to the given size.
font_em: ?

# The font's ascent and descent. Used to calculate the baseline.
font_ascent: ?
font_descent: ?