Network

MTU MSS Calculator

Calculate effective payload and TCP MSS from MTU and tunnel overhead.

Last validated: 2026-02-14

MTU MSS Calculator estimates TCP MSS from link MTU and protocol overhead. It is useful when diagnosing fragmentation, tunnel overhead, and throughput drops. The tool helps you choose safe MSS clamping values for VPN and edge configurations. Use it before rolling out MTU-related network changes.

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Input Pattern

Enter values in the left panel, keep units explicit, run the calculation, then copy or share the result. Invalid fields are highlighted immediately.

MTU/MSS Inputs

Result

IP header: 20 bytes

Transport header: 20 bytes

Tunnel overhead: 0 bytes

Max payload: 1460 bytes

TCP MSS: 1460 bytes

How to use this tool

Enter path MTU and protocol options that affect overhead.
Run the calculator to compute effective MSS.
Apply suggested values in test, then validate with packet captures.

Worked Example

Auto-generated from the tool's current default or entered inputs.

Example Inputs

Mtu: 1500
Ip version: ipv4
Transport: tcp
Tunnel: none
Ip header: 20
Transport header: 20
Tunnel overhead: 0
Mss: 1460

Expected Outputs

Mtu: 1500
Ip header: 20
Transport header: 20
Tunnel overhead: 0

Interpretation

Mtu is 1500. Use this as a decision input, not as a standalone conclusion.
Ip header is 20. Use this as a decision input, not as a standalone conclusion.
Transport header is 20. Use this as a decision input, not as a standalone conclusion.
Confirm unit consistency and operational constraints before applying this result in production or field conditions.

Scenario Compare (A vs B)

Use this to compare two input sets and quantify change in key outputs.

Scenario A

Mtu

Ip version

Transport

Tunnel

Ip header

Transport header

Tunnel overhead

Mss

Scenario B

Mtu

Ip version

Transport

Tunnel

Ip header

Transport header

Tunnel overhead

Mss

Formula References

IPv4/IPv6 addressing rules and common protocol arithmetic.
DNS/WHOIS/network calls depend on external resolvers and current network state.

Assumptions

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