How long did baby last in newborn size diapers? I am looking at stocking up - how many newborn size should I buy?

My baby is 2 wks old still using NB and he is on the big side.. I got him these 2 brands Peekapoo and Rascal & friends which I highly recommend for heavy weight coz its super absorbent and long lasting. Both in NB so basically 2 packs for NB 80 pcs+ Small samples I got in total about 180 pieces.