Network Engineer
TCP Window Calculator
Use this tcp window calculator entirely in your browser.
TCP window target: 5,000,000 bytes.
Bandwidth-delay product: 1,000 Mbps × 40 ms.
Calculations happen locally in your browser.
How to use this calculator
- Enter the labelled values and review the live result.
- Review the live result and use Copy result when you need to share it.
How the calculation works
Target bits per second multiplied by round-trip seconds gives bits in flight, then division by eight gives bytes.
Formula
Target bits per second multiplied by round-trip seconds gives bits in flight, then division by eight gives bytes.
Step-by-step calculation
- Enter the labelled values and review the live result.
- Target bits per second multiplied by round-trip seconds gives bits in flight, then division by eight gives bytes.
- Check the displayed result, then copy it if needed.
Worked example
1 Gbps over a 40 ms round trip needs about 5 MB in flight.
Methodology and review
Who this is for
Engineers estimating in-flight data for a TCP path.
Inputs and units
- Target throughput
- Round-trip latency
Method
Bandwidth-delay product equals throughput in bits per second multiplied by round-trip time in seconds; the result is converted to bytes for the suggested in-flight window.
Worked example
1 Gbps across 40 ms has a bandwidth-delay product of 5 MB.
Assumptions
- Round-trip time and target throughput are stable.
- The calculation describes one idealised TCP flow.
Common mistakes
- Entering one-way latency
- Applying the value without checking TCP scaling
Limitations
- Loss, congestion control, scaling, buffers, and operating-system limits affect achieved throughput.
- Do not treat the result as a universal socket setting.
How this tool was checked
Tests verify unit conversion and known bandwidth-delay product examples.
Reference sources
Related tools
Calculation review: 21 August 2026. Published by Goldwave Dynamics Limited. This is an internal product review, not an independent certification.
Risk guidance
Frequently asked questions
Does this tool send my inputs anywhere?
No. The interactive calculation runs in your browser and this site does not submit tool inputs to a backend.
How should I use the result?
Check that the entered units and values match your situation, especially around dates, breaks, and rounding.
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