In ImageMagick, one gets a better SVG rendering if one uses Inkscape or RSVG with ImageMagick than its own internal MSVG/XML rendered. RSVG is a delegate that needs to be installed with ImageMagick. If Inkscape is installed on the system, ImageMagick will use it automatically. I use Inkscape in ImageMagick below.
There is no "magic" parameter that will do what you want.
But, one can compute very simply the exact density needed to render the output.
Here is a small 50x50 button when rendered at the default density of 96:
convert button.svg button1.png
Suppose we want the output to be 500. The input is 50 at default density of 96 (older versions of Inkscape may be using 92). So you can compute the needed density in proportion to the ratios of the dimensions and the densities.
512/50 = X/96
X = 96*512/50 = 983
convert -density 983 button.svg button2.png
In ImageMagick 7, you can do the computation in-line as follows:
magick -density "%[fx:96*512/50]" button.svg button3.png
or
in_size=50
in_density=96
out_size=512
magick -density "%[fx:$in_density*$out_size/$in_size]" button.svg button3.png