Output
Effective MTU and TCP MSS, bytes
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MTU & MSS Calculator
Calculate TCP MSS from MTU, IP version and extra tunnel overhead.
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MTU & MSS Calculator · At a glance
Quick answer: Calculate TCP MSS from MTU, IP version and extra tunnel overhead. With MTU 1500 and no tunnel, base IPv4 MSS is 1460 bytes and IPv6 MSS is 1440 bytes.
MTU & MSS Calculator
The test loads when you open it. Device access is requested only after you choose to start.
Detailed guide
How to use this tool
- Enter link MTU, IP version and any tunnel overhead.
- Read effective MTU and the base TCP MSS estimate.
Input
Values and units entered in the calculator
Browser requirement
Local arithmetic; no hardware access
Processing
Runs on your device; no tool-result upload
How it works and what the result means
The result is a mathematical estimate under the stated formula. It does not read your hardware or change system settings.
Reading the result
With MTU 1500 and no tunnel, base IPv4 MSS is 1460 bytes and IPv6 MSS is 1440 bytes. Extra headers can reduce payload.
Worked example and assumptions
effective MTU = link MTU − tunnel overhead; TCP MSS = effective MTU − IP header − 20
MTU 1500 with no tunnel: IPv4 MSS = 1460 bytes; IPv6 MSS = 1440 bytes.
The TCP base header is assumed. Options and extra encapsulation can reduce usable payload.
MTU 1500 with no tunnel: IPv4 MSS = 1460 bytes; IPv6 MSS = 1440 bytes.
The TCP base header is assumed. Options and extra encapsulation can reduce usable payload.
What to check next
Keep tunnel overhead in bytes and avoid subtracting the same encapsulation twice. Confirm the actual path separately.
Keep consistent units and compare the assumptions with your actual game, display or network configuration.
Frequently asked questions
Does this discover the path MTU automatically?
No. It performs header arithmetic on your inputs. It does not send discovery probes or change a network adapter setting.
How do I start the MTU & MSS Calculator?
Enter your own values and press Calculate. Units are shown beside each field; invalid or impossible values are rejected.
Does this tool require a download or an account?
No. Open the interactive tool above in a modern browser. The instructions and explanations are available even with JavaScript disabled; running a test needs JavaScript.
Will this change my device or game settings?
No. The calculator or generator only creates a result for you to review. It does not detect or modify your hardware, operating system or game configuration.
Why can another calculator show a different answer?
Compare the units, rounding and assumptions. The same inputs and formula give the same result here; background CPU load does not change the mathematics.