How to understand and give the layout designer the spacing between letters if he is in illustrator, for example, 67?

Question

HTML

Essence of the question;
font 45 we multiply by 1.5 we get 67.5
in illustrator we give the value I
attach a photo
how to set the value here in the code? letter-spacing:

Answer 1

(your value * font-size) / 1000