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MTU & TCP MSS Calculator

Calculate inner MTU, advertised TCP MSS, and payload budget with explicit encapsulation overhead. Work locally without uploading network information.

Runs entirely on your deviceNo uploads, accounts, cookies, or personal tracking.

Calculate MSS budget

Local processing · no input storage

Network tools
Select the format or assumption to use.
Enter the value to evaluate.
Bytes removed from the path IP MTU for tunneling. Enter 0 for a direct path.
0–40 bytes in multiples of 4. These reduce actual payload, not the advertised MSS.

Uses fixed IP/TCP headers. Does not model IP options, IPv6 extension headers, or discover the live path MTU.

Enter your data, then select calculate mss budget.

Technical reference: RFC 6691

1. Add your data

Enter your network data or load the worked example.

2. Choose the result

Calculate MSS budget and review the result and assumptions.

3. Save it locally

Copy the result or download it for your engineering workflow.

About this tool

Use MTU & TCP MSS Calculator without an upload

Calculate inner MTU, advertised TCP MSS, and payload budget with explicit encapsulation overhead. Work locally without uploading network information.

The operation runs in the current browser tab. Tool input is not included in aggregate analytics, and the standalone download makes no analytics requests.

Network toolsDeveloper tools