What is the maximum size in bytes of an ethernet packet?

The maximum transmission unit (MTU) for Ethernet, which is the largest size of an Ethernet packet or frame that can be sent over the network, is typically 1500 bytes. This size does not include the Ethernet frame's preamble and start frame delimiter but does include all other headers and the payload. Ethernet's MTU of 1500 bytes is a standard for most Ethernet networks, especially those conforming to the IEEE 802.3 standard.References:

IEEE 802.3-2012, "Standard for Ethernet".