Garment Seam Gather Ratio Tool

Description

Subtract the same allowances from both and divide usable lengths.

Ease, gathering and stretch compare lengths on a chosen baseline. Extra-length ratio, finished/flat ratio and extension from relaxed length are different conventions, so the denominator must be explicit.

Subtract the same allowances from both and divide usable lengths.

When to use this tool

Use Garment Seam Gather Ratio when you need one stated ease, gauge or stretch relationship.

How to use the tool and how it works

Enter ungatheredLength, finishedLength, seamAllowanceEachEnd. Use the units and conventions below.
Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
Read usableUngathered, usableFinished, gatherRatio. Use the output convention below.

Require nonnegative end allowance, ungathered length at least twice it and finished length strictly greater than twice it. Subtract the same allowances from both and divide usable lengths.^[1]

Input field	Meaning and units	Accepted input
ungatheredLength	Ungathered Length	Required. Finite number.
finishedLength	Finished Length	Required. Finite number.
seamAllowanceEachEnd	Seam Allowance Each End	Required. Finite number; minimum 0.

Output field	Interpretation	Returned shape
usableUngathered	Usable Ungathered	Required. Finite number.
usableFinished	Usable Finished	Required. Finite number.
gatherRatio	Gather Ratio	Required. Finite number.

json

{
  "input": {
    "ungatheredLength": 104,
    "finishedLength": 54,
    "seamAllowanceEachEnd": 2
  },
  "output": {
    "usableUngathered": 100,
    "usableFinished": 50,
    "gatherRatio": 2
  }
}

Limitations and assumptions

The gather ratio can be below one because ungathered is not required to exceed finished. No fabric behavior, pattern suitability or fit is inferred.
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

Test the intended material and review the complete pattern fit. Account for recovery, shrinkage, directional stretch and construction instead of interpreting a length ratio as guaranteed comfort or suitability.

References

Calculation and input contract: fashion/garment-seam-gather-ratio — tool.io

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