Page size:      624 x 312 pts

$ identify -verbose some.pdf | grep "Print size"
Print size: 8.26389x11.6944

$ units -t '8.26389 inch' 'mm'
  209.90281

/MediaBox [0 0 595 842]
/MediaBox[0 0 595 842]
/MediaBox[ 0 0 595.32 841.92]

cat test.pdf | egrep -ao "/MediaBox ?[ ?[0-9]+ [0-9]+ [0-9]+(.[0-9]+)? [0-9]+(.[0-9]+)?]" | head -1