Rather than trying to compute it, why not just tell the SVG text to center itself? I found a reference here:
http://www.w3.org/TR/SVG/text.html#TextAlignmentProperties.

...roboticus

When your only tool is a hammer, all problems look like your thumb.

Update: s/it/itself/ to clarify intent.

In reply to Re: SVG text width calculation by roboticus
in thread SVG text width calculation by Anonymous Monk

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