Live tool

MTU / MSS Helper

Calculate effective MTU, TCP MSS, and clamp-ready values across IPv4 and IPv6 networking scenarios with practical tunnel overhead presets.

Live 3 calculations Network Tools Helper Networking MTU MSS
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Input

Calculate TCP MSS from MTU or work backward from a target MSS to the required MTU, with IPv4 or IPv6 header assumptions and tunnel overhead presets.

Enter the starting MTU before tunnel or protocol overhead is removed.
Preset overhead is combined with any custom overhead you add below.
Add extra bytes on top of the selected preset when your path has additional encapsulation or margin requirements.
Reset

Result

Effective MTU, TCP MSS, overhead breakdown, and clamp-ready values for practical networking workflows.

Mode MTU → MSS
IP version IPv4
Total overhead 0 bytes
TCP MSS 1,460 bytes
Base / interface MTU 1,500 bytes
Effective IP MTU 1,500 bytes
Preset overhead 0 bytes
Custom overhead 0 bytes
IP header 20 bytes
TCP header 20 bytes

What this means

Starting from a base MTU of 1,500 bytes, the tool removed 0 bytes of overhead and then subtracted standard IPv4 and TCP headers to calculate a TCP MSS of 1,460 bytes.

The selected preset "No extra overhead" contributes 0 bytes, and custom overhead contributes 0 bytes, for a total overhead of 0 bytes.

IPv4 is calculated with a 20-byte IP header and a 20-byte TCP header in this version of the tool.

A practical clamp-ready TCP MSS value for this scenario is 1,460. With no additional modeled tunnel overhead, the result reflects a straightforward IPv4 path calculation.

Calculation breakdown

  1. Start with base / interface MTU: 1,500 bytes.
  2. Subtract total overhead (0 bytes) to get effective IP MTU: 1,500 bytes.
  3. Subtract IPv4 header (20 bytes): 1,500 - 20 = 1,480 bytes.
  4. Subtract TCP header (20 bytes) to get estimated TCP MSS: 1,460 bytes.

Common presets

Ethernet 1500 / IPv4 Ethernet 1500 / IPv6 PPPoE 1492 / IPv4 WireGuard over 1500 / IPv4 VXLAN over 1500 / IPv4 IPsec ESP / IPv6

MTU / MSS quick guide

Practical notes for effective MTU and TCP MSS sizing.

Base MTU

Base or interface MTU is the starting packet size before extra protocol or tunnel overhead is subtracted.

Effective IP MTU

Effective IP MTU is what remains for the IP packet after preset and custom overhead bytes are removed.

TCP MSS

TCP MSS is the maximum TCP payload after IP and TCP headers are accounted for inside the effective IP MTU.

Calculation assumptions

The numbers below describe exactly what this version of the tool assumes.

  • IPv4 header is treated as 20 bytes.
  • IPv6 header is treated as 40 bytes.
  • TCP header is treated as 20 bytes.
  • Preset overhead values are practical planning estimates.
  • Custom overhead is added on top of the preset.
  • Real paths may vary due to implementation details and optional protocol fields.

Common use cases

Typical network engineering and troubleshooting scenarios.

Size safe TCP MSS values for VPN, overlay, or tunneled paths where encapsulation reduces payload space.

Validate MSS clamping assumptions for firewalls, edge devices, or hybrid network paths.

Compare IPv4 and IPv6 header impact under the same base MTU and overhead profile.