Standard 3.5" × 2" double-sided. Page 1 = front, Page 2 = back (with QR). Hand the PDF to Office Depot and ask for double-sided full-color business cards.
Tip: ask Office Depot for "double-sided, full-color, standard 3.5×2 business cards." If they require bleed, request a 1/8" trim — the navy background extends to the edge.