Free network utility
MTU and MSS Calculator
Estimate TCP MSS from an MTU for IPv4 or IPv6 and common tunnel overheads.
What this tool calculates
Estimate TCP MSS from an MTU for IPv4 or IPv6 and common tunnel overheads. The calculation is designed for practical home and small-office network planning.
Important limitations
Results depend on the values and settings you provide. Verify changes with the router manufacturer, internet provider, or an authorized network administrator before applying them to an important network.
Privacy and responsible use
This calculation runs locally in your browser. RouterNAT does not receive or save the values entered into this tool. Use the result only for lawful network administration and troubleshooting.
Related RouterNAT guides
To understand WAN and public-address differences, read the complete CGNAT detection guide before changing NAT or port-forwarding settings.
How to use this result
Verify important changes against your router manual, ISP documentation, or an authorized network administrator. This utility provides planning guidance and does not connect to, scan, or modify your router.