Change SVG units from "px" to "mm"

When I save an SVG from an illustration as "SAVE AS", the width and height are set to "px", is there any way to make the units "mm"?

ex)

<svg version="1.1" id="Layer_1" xmlns:x="&ns_extend;" xmlns:i="&ns_ai;" xmlns:graph="&ns_graphs;"
xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px" width="176px" height="176px"
viewBox="0 0 176 176" enable-background="new 0 0 176 176" xml:space="preserve">