What it does
Given an MTU (Maximum Transmission Unit, typically 1500 for Ethernet), this tool calculates:
- The maximum ICMP ping payload size that fits in a single, unfragmented packet.
- How many fragments a packet of a given total size would be split into.
Useful for diagnosing tunnel/VPN MTU issues (ping -f -l <size> on Windows, ping -M do -s <size> on Linux).
Try it
How it works
- IPv4 header: 20 bytes (no options)
- ICMP header: 8 bytes
- Max unfragmented ping payload =
MTU - 20 (IP) - 8 (ICMP) - To test the real path MTU with the "don't fragment" flag, ping using that payload size:
- Windows:
ping -f -l <payload> <host> - Linux/macOS:
ping -M do -s <payload> <host> - Fragmentation estimate: if you send a larger packet without DF set, it gets split into
ceil(totalSize / (MTU - 20))fragments (each fragment re-uses one 20-byte IP header, but not the ICMP header after the first fragment).
Everything is computed locally in your browser.