How to convert Photoshop tracking to px for css?

Question

Adobe Photoshop

What unit of measurement does Photoshop use to set font tracking?
How to convert this size to simple px?

Answer 1

I guess
40 is 0.4px

Answer 2

The formula for calculating letter-spacing in em is:
X / 1000 = Y
Where X is the spacing value in Photoshop and Y is the same value expressed in em for CSS.
X * S / 1000 = P
Where X is the spacing value in Photoshop, S is the font size in pixels (when working at 72 dpi), and P is the spacing value for CSS.
Some browsers calculate the spacing value in pixels even if it is given in em: it rounds up to an integer value.

Answer 3

I hope I explained it clearly =)

I hope it's clear how to search in Google
htmlbook.ru/css/letter-spacing