The basic IPv4 header has a fixed size of 20 octets; the variable-length options field increases the size of the total IP header. IPv6 contains fields similar to 7 of the 12 IPv4 basic header ...

With IPv6, the Payload Length only counts the size of the data carried in the IP packet; the size of the IPv6 header (40 bytes) isn't included. Ethernet can carry packets up to 1500 bytes long.