MTU Calculator

Summary

Select your link type and encapsulation layers to instantly calculate the optimal MTU, payload size, and fragmentation overhead.

How it works

1. Select your physical link type (Ethernet, Wi-Fi, etc.) or enter a custom physical MTU.
2. Check all encapsulation layers active on your path (PPPoE, GRE, IPsec, VXLAN, MPLS, etc.).
3. The tool subtracts each layer's fixed header overhead from the physical MTU.
4. The result shows the usable inner payload MTU and total overhead bytes.
5. Use the recommended MSS value for TCP performance tuning on your router or firewall.
6. Adjust IPv4 or IPv6 mode to account for the correct IP header size.

Use cases

• Find the correct MSS clamp value for PPPoE broadband connections.
• Tune MTU on IPsec or WireGuard VPN tunnels to prevent packet fragmentation.
• Calculate inner payload size for VXLAN overlay networks in data centers.
• Verify MTU settings when stacking GRE over IPsec over PPPoE.
• Troubleshoot slow file transfers or broken websites caused by MTU black holes.
• Plan MPLS label stack depth and its impact on usable MTU.
• Document correct MTU for cloud VPN configurations (AWS, Azure, GCP).
• Validate MTU settings before deploying SD-WAN or MPLS circuits.

Frequently Asked Questions