What is MSS in TCP?

MSS = Maximum Segment Size - the largest data payload TCP sends in one segment, typically 1,460 bytes on IPv4/Ethernet (1500 MTU - 20 IP - 20 TCP).

MSS = Maximum Segment Size

The largest amount of data (in bytes) that TCP will send in a single segment.

Typical value: 1,460 bytes

Calculation:

• Ethernet MTU: 1,500 bytes
• Minus IP header: 20 bytes
• Minus TCP header: 20 bytes
• = 1,460 bytes for data

When negotiated: During the three-way handshake (in TCP options)

Memory tip: MSS is about "Maximum Stuff to Send" in one piece.

Go deeper:

• Maximum segment size — Wikipedia reference for the MSS option, its defaults, and how it differs from the MTU.
• RFC 9293 §3.7.1 — Maximum Segment Size Option — the authoritative definition of how MSS is advertised during the handshake.