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 Maximum Segment Size from link MTU and protocol overhead. MTU is the largest packet size a link can carry without fragmentation, while MSS is the largest TCP payload segment after subtracting IP and TCP headers. Encapsulation layers such as PPPoE, VPN tunnels, GRE, VXLAN, or IPsec consume additional bytes, reducing the payload that fits inside the same physical frame. If MSS is too high, packets may fragment or fail when path MTU discovery is blocked; if it is too low, throughput can suffer from unnecessary overhead. This tool is useful for diagnosing tunnel performance, intermittent web failures, and TCP clamping settings, but live paths should be verified with packet captures or network tests.

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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 MTU, IP version, Transport, Tunnel for the mtu mss calculator, keeping units, dates, or text format consistent with the form labels.
Confirm address formats, masks, ports, or hostnames match the network environment you are checking.
Click "Run the tool" and review MTU/MSS Inputs, Result for the primary output.
Compare the output with device, provider, or DNS authority settings before applying a live network change.

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.

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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MTU MSS Calculator

Input Pattern

MTU/MSS Inputs

Result

How to use this tool

Worked Example

Example Inputs

Expected Outputs

Interpretation

Formula References

Assumptions

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