TCP Window Scale Effective Capacity Tool

Description

Multiply window by 2 raised to shift, except that synSegment selects an unscaled window.

TCP advertises a receive window in a 16-bit field. A negotiated scale expands its interpretation for one direction, while SYN segments use the unscaled field.

Multiply window by 2 raised to shift, except that synSegment selects an unscaled window.

When to use this tool

Use TCP Window Scale Effective Capacity when you need a window capacity under an explicit scaling convention.

How to use the tool and how it works

Enter window, shift, synSegment. Use the units and conventions below.
Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
Read effectiveWindow. Use the output convention below.

Multiply window by 2 raised to shift, except that synSegment selects an unscaled window. Window is 0-65535 and shift is 0-14.^[1]

Input field	Meaning and units	Accepted input
window	Window	Required. Safe integer; minimum 0; maximum 65535.
shift	Shift	Required. Safe integer; minimum 0; maximum 14.
synSegment	Syn Segment	Required. Boolean.

Output field	Interpretation	Returned shape
effectiveWindow	Effective Window	Required. Safe integer.

json

{
  "input": {
    "window": 1000,
    "shift": 4,
    "synSegment": false
  },
  "output": {
    "effectiveWindow": 16000
  }
}

Limitations and assumptions

The calculation does not infer a peer's negotiated shift or track TCP state.
Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Numeric signed-zero results are exported as zero.

Alternative or Complementary methods

Inspect both handshake directions to establish the negotiated shift before interpreting later window fields.

References

Calculation and input contract: network/tcp-window-scale-effective-capacity — tool.io

Similar or alternative tools

TCP Window Scaling One Direction
Multiply the 16-bit window by 2 raised to shift, with shift from 0 through 14.
TCP Sequence Syn Fin Consumption
Add payloadBytes and one sequence position for each true SYN and FIN flag.