THE NUMBERS, EXPLAINED
How to use this calculator.
Equal-width straight strips are joined end to end. Each join consumes two seam allowances. Enter a ratio of at least one; the result includes the stated end allowance. Strip width and fabric yardage are outside this length-only model.
Start with your inputs
Enter finished trim length (cm), gathering ratio, usable strip length (cm), seam allowance at each joining edge (cm), combined allowance for the two exposed ends (cm). Keep amounts in the units shown on each field. The example is a starting point, not a recommended value.
| Input | Example value |
|---|---|
| Finished trim length (cm) | 300 |
| Gathering ratio | 2 |
| Usable strip length (cm) | 110 |
| Seam allowance at each joining edge (cm) | 1 |
| Combined allowance for the two exposed ends (cm) | 4 |
A worked example
With the example inputs above, ungathered usable length (cm) is 600. Change the inputs to explore your own scenario.
| Result | Example answer |
|---|---|
| Ungathered usable length (cm) | 600 |
| Strip count | 6 |
| Strip joins | 5 |
| Gross cut length (cm) | 660 |
| Excess after joins and allowances (cm) | 46 |
How this is calculated
Ungathered usable length (cm)
Finished trim length × gathering ratio.
Strip count
Choose the smallest n satisfying n × strip length − 2 × seam allowance × (n−1) ≥ gathered length + end allowance.
Strip joins
Strip count minus one.
Gross cut length (cm)
Strip count × strip length.
Excess after joins and allowances (cm)
Gross length minus join losses, end allowance and ungathered required length.
Symbols and units
- a
- Finished trim length (cm)
- b
- Gathering ratio
- c
- Usable strip length (cm)
- d
- Seam allowance at each joining edge (cm)
- e
- Combined allowance for the two exposed ends (cm)
Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.
Assumptions and limits
Equal-width straight strips are joined end to end. Each join consumes two seam allowances. Enter a ratio of at least one; the result includes the stated end allowance. Strip width and fabric yardage are outside this length-only model.
Calculations use the values you enter. Blank or invalid inputs show an error instead of silently substituting zero. Results are displayed to useful precision; calculations retain the underlying numeric precision.
Questions about this tool
What does the result tell me?
Ungathered usable length (cm); Strip count; Strip joins; Gross cut length (cm); Excess after joins and allowances (cm). The result applies to the method and inputs described above. Check the units and assumptions before using it in a decision.
Why might another calculator differ?
Differences in units, rounding, timing or model definitions can produce different answers. Compare the input definitions and the method, rather than only the final number. For this tool: Equal-width straight strips are joined end to end. Each join consumes two seam allowances. Enter a ratio of at least one; the result includes the stated end allowance. Strip width and fabric yardage are outside this length-only model.
Are my inputs stored or sent to AI?
Calculations on this page happen in your browser. The separate AI question finder sends its submitted conversation to OpenAI; these calculator fields are not sent. Favourites and recent tool names are stored locally. A shared link contains the inputs you choose to include.
Further reading
OpenStax: geometric formulas and arithmetic ↗
Background reading; this does not imply endorsement or independent review of SumFizz.
Review status
Software example and browser checks are recorded in our quality report. No external expert review is claimed. Created with coding assistance; calculations run as ordinary browser code.
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