MTU & TCP MSS Calculator
Calculate common TCP maximum segment size from an IP MTU and selected IPv4 or IPv6 header assumptions.
What this tool calculates
MTU & TCP MSS Calculator is designed to give a direct answer from the values entered above. The main inputs on this page are MTU (bytes), IP version. The result is intended to be readable immediately, with the explanation below available when you need to verify the method.
Method and calculation basis
The result is calculated from the labelled inputs shown above using the operation named by the tool. Inputs are normalised to compatible units before arithmetic where the page supports multiple units.
Worked examples
Known private network
Use a familiar 192.168.x.x subnet to verify mask and host-range behaviour.
Boundary case
Check prefix boundaries such as /24, /30 and /32 to understand how the available address space changes.
Understanding the result
The output should be read in the units shown beside the result. If you are comparing alternatives, keep all unchanged assumptions identical and alter one input at a time. That makes it easier to see which value is responsible for the difference.
Assumptions, edge cases and accuracy
Address arithmetic does not prove reachability. Routing, VLANs, NAT, DNS, host configuration and firewall policy can all change what actually works on a network.
Sources and methodology
- IETF RFCs — Internet addressing, CIDR and protocol definitions
- IANA — Protocol parameters, port/service registries and address information
Method reviewed for Instant Solvers V10.0 · October 2026. If you find a calculation or explanation that needs correcting, use the site Contact page and include the tool URL and the values you entered.