Visual packet size calculator

Parent interface MTU:
Calculation mode:
Encapculated protocol MTU (subtract overhead from the parent interface MTU)
Frame size (add overhead to payload size)
Header size (overhead):
Protocols (click protocol buttons one or more time to add):


Knowing the encapsulation overhead of your protocol stack is important for configuring VPN tunnels. You need to set the tunnel interface MTU correctly, to avoid excessive packet fragmentation.

This tool allows you to easily see what each protocol adds to your packet. Click protocol buttons to add protocols to the stack. Some protocols have additional options, e.g. if you click Ethernet, you will see VLAN and QinQ header option checkboxes.

For example, if you want the TCP MSS for IPv6 in GRE over IPv4, click: IPv4, GRE, IPv6, TCP.

Header sizes for VXLAN, LISP, and WireGuard include UDP, and STT includes TCP, because these protocols never use another L4 protocol. Everything else is pure header size exclusing any outer or inner protocols, e.g. “MPLS” is the size of a single MPLS label (4 bytes).