Not all vector programs see things the same way. Here are 3 of the most popular.
While SVG files can be defined in real world units like mm and inch, but some vector programs convert these units into px (pixels). Unfortunately, some programs assume different pixel density.
Illustrator assumes 72 pixels per inch
Inkscape assumes 96 pixels per inch
Corel Draw assumes 72 pixels per inch
I have found that the easiest way to fix this when opening SVG's in Inkscape that were created in Illustrator, is go to to:
File>Document Properties>display units = inches
Then change the file's scale to 72 pixels per inch.