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MTU Calculator

A specialized MTU and MSS calculator for calculating maximum transmission unit settings and packet overhead across various protocols including VPNs (IPsec, OpenVPN, WireGuard), PPPoE, GRE tunnels, and VLAN tagging. Perfect for network engineers optimizing VPN performance, ISP technicians diagnosing DSL connections, or anyone experiencing packet fragmentation issues. Select your connection type and instantly see the optimal MTU, calculated TCP MSS, overhead breakdown, and ready-to-use configuration commands for Linux, Windows, and macOS. Use MTU Calculator when you need answers fast during debugging, reviews, or incident triage. Paste your input, validate the output, then copy results into tickets or docs in seconds. Most processing runs in your browser, so you can test safely without unnecessary data exposure.

How to Use This Tool

  1. Select Connection Type - Choose from Ethernet, PPPoE, VPN protocols, GRE, VLAN, or enter a custom MTU
  2. Click Calculate - View recommended MTU, TCP MSS, protocol overhead breakdown, and payload size
  3. Apply Settings - Copy the provided OS-specific commands to configure your network interface

Why This Method?

MTU (Maximum Transmission Unit) is the largest packet size that can traverse a network path without fragmentation. Standard Ethernet uses 1500 bytes, but encapsulation protocols add overhead: PPPoE adds 8 bytes (1492 MTU), OpenVPN adds 80 bytes (1420 MTU), IPsec adds 58 bytes (1442 MTU), and WireGuard adds 80 bytes (1420 MTU). Incorrect MTU settings cause packet fragmentation, leading to retransmissions, latency spikes, and reduced throughput.

TCP MSS (Maximum Segment Size) is the MTU minus IP header (20 bytes) and TCP header (20 bytes). For example, a 1500-byte MTU results in a 1460-byte MSS. When packets exceed the path MTU, they're fragmented into smaller pieces, but some firewalls block ICMP Path MTU Discovery messages, causing black-hole routing where packets disappear silently.

VPN users commonly experience slow connections because their VPN software doesn't automatically adjust MTU for the tunnel overhead. By calculating and setting the correct MTU, you eliminate fragmentation, improving VPN speeds by 20-40% in real-world scenarios. This tool provides the exact values and commands needed for optimal performance.