Network MTU & TCP MSS Calculator

Calculate IP and transport payload, TCP MSS, and packet efficiency with configurable encapsulation overhead.

Local browser processing

Addresses and calculation inputs stay in this browser. They are not uploaded, resolved, scanned, or sent to analytics.

Link MTU

IP version

IPv4

Transport

TCP

Additional tunnel/encapsulation overhead

bytes

Result

Enter values and run the tool to see the local result.

How MTU and MSS are related

MTU limits the IP packet carried by a link. TCP MSS is the remaining TCP payload after subtracting the IP header, TCP header, and any additional encapsulation overhead. This calculator also handles UDP payload and keeps tunnel overhead explicit instead of assuming one universal value.

How to calculate MTU payload and MSS

Enter the link MTU and choose IPv4 or IPv6 plus TCP or UDP.
Add the exact overhead introduced by VPN, PPPoE, VLAN, GRE, or another encapsulation in your path.
Review the header sizes, maximum payload, TCP MSS when applicable, and payload efficiency.

Header and tunnel assumptions

The calculator uses base IPv4, IPv6, TCP, and UDP header sizes. IP options, IPv6 extension headers, TCP options, offload behavior, nested tunnels, and path-MTU discovery can change the operational result.

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MTU and MSS questions

What is the TCP MSS for a 1500-byte IPv4 MTU?: With a 20-byte IPv4 header and 20-byte TCP header and no extra overhead, the TCP MSS is 1460 bytes.
Why is IPv6 TCP MSS smaller for the same MTU?: The base IPv6 header is 40 bytes instead of the base 20-byte IPv4 header, leaving 20 fewer bytes before other options or overhead.
Does UDP have MSS?: No. MSS is a TCP concept; the calculator shows maximum UDP payload after the selected headers and overhead.
Does this discover path MTU?: No. It performs local arithmetic and does not send packets or probe a network path.

MTU and MSS questions

What is the TCP MSS for a 1500-byte IPv4 MTU?

With a 20-byte IPv4 header and 20-byte TCP header and no extra overhead, the TCP MSS is 1460 bytes.

Why is IPv6 TCP MSS smaller for the same MTU?

The base IPv6 header is 40 bytes instead of the base 20-byte IPv4 header, leaving 20 fewer bytes before other options or overhead.

Does UDP have MSS?

No. MSS is a TCP concept; the calculator shows maximum UDP payload after the selected headers and overhead.

Does this discover path MTU?

No. It performs local arithmetic and does not send packets or probe a network path.