What does the TCP header size typically measure?

The TCP header size typically measures 20 bytes. This size accounts for the essential fields that are necessary for TCP communication, such as source and destination port numbers, sequence and acknowledgment numbers, and control flags. The minimum TCP header includes these vital fields, ensuring that segments of data can be properly assembled and transmitted over a network.

It is important to note that although the base TCP header is 20 bytes, additional options may lead to an increase in size through the use of options fields, which can add extra bytes as necessary. However, without any options included, the standard header remains at the 20-byte size, making it the correct answer in this context.