How to calculate viewBox for text in SVG?

Question

css

I want to make the SVG text, and then use it as a background-image.
I will insert from a sprite or inline.
But, I can not understand how the viewBox is calculated.
For example, how to calculate the size of the viewBox for the text "Hello", in the example below, I put them at random.

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 500 35">
 <text x="0" y="50" font-family="Verdana" font-size="35px" fill="gray">Привет</text> 
</svg>

Haven't figured out how to use styles yet:
font-stretch - Compress and stretch text. Possible values: normal (default) | wider | narrower | ultra condensed | extra condensed | condensed | semi-condensed | semi-expanded | expanded | extra-expanded | ultra-expanded
text-anchor - Alignment of text relative to the beginning of the line. Possible values: start (default), middle, end
but rather the last questions will be closed if you deal with the viewBox.