IPv4 Fragment Size and Offset Calculator
Plan mathematical IPv4 fragment sizes for a fixed 20-byte header and entered MTU/DF flag.
YOUR CALCULATION
Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Keep nonfinal fragment payloads in multiples of eight bytes and no larger than MTU minus the fixed header. Reassemble offsets against the original payload.
Nonfinal payload=8×floor((MTU−20)/8); fragment offset=preceding payload bytes/8
Worked example
Total length 4000 and MTU 1500 give payload chunks 1480,1480,1020; fragment total lengths 1500,1500,1040 and offsets 0,185,370.
Assumptions and input details
IPv4 only with fixed IHL=5 (20 bytes), no options and no existing fragment offset. Total length 20–65535 bytes. DF prevents splitting when MTU is insufficient. No real packets are created, sent or captured. First 199 and final fragment rows are shown if more than 200 exist. Payload overhead is distinguished from original total length.
References: IETF RFC 791: fragmentation and offsets
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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