Payload size from MTU and encapsulation

Network administrators can calculate the available payload when encapsulation changes the amount that fits within the chosen MTU.

Work out the payload size supported by the selected encapsulation and MTU, providing a clear figure for preparing coherent parameters.

How to use

Enter the link MTU in the first field, using the value reported by your equipment or network plan.
Specify the encapsulation in use, choosing one of the types mentioned in the input hint.
Run the calculation to derive the payload size supported by that MTU.
Read the result and check whether it matches the packet size you expect for your setup.
Change the MTU or encapsulation to compare scenarios before applying settings to a device.

Example

With an input such as 1500 followed by ipv4, the calculator shows the payload left after the relevant header is accounted for. Look at the returned value, then try another encapsulation to see how the available room changes.

Input

1500
ipv4

Limits and formats

The calculation uses the values and encapsulation you provide; it does not measure the real MTU of the link.
A wrong MTU can cause fragmentation or dropped packets, so validate the figure with a suitable network test.
Only the encapsulation types listed in the field can be calculated; an unlisted type has no direct option here.
The payload shown reflects the selected encapsulation only, not additional overhead from applications or tunnels.

Where processing happens

The arithmetic happens entirely in your browser. The MTU and encapsulation you type stay on the page and are not transmitted. That makes it easy to compare several values in a row without an account, and no previous calculation is stored for later.

Frequently asked questions

How is payload different from MTU?

MTU is the largest data unit allowed on the link. Payload is what remains for your data after the headers required by the chosen encapsulation are subtracted. This calculator performs that subtraction for the values you enter.

What if my encapsulation is not listed?

The tool only offers the types shown in the input hint. If your setup uses something else, this page cannot calculate it directly. Check your vendor documentation or use a calculator that covers that specific encapsulation.

Can I apply the result to a router configuration?

Treat it as a starting point and confirm it on the live network. The effective MTU may vary with the provider, tunnel or hardware. A fragmentation test or path discovery command is still needed before you commit the value.