Worked examples
Check the distances from one shared centre.
These are numerical panel examples, not body-size or fit recommendations. All inputs and output lengths use centimetres; all displayed geometry is approximate.
A 72 cm chosen opening and 55 cm finished length
Choose opening circumference 72, finished radial length 55, inward waist allowance 1 and outward hem allowance 1.5.
- The stitched opening radius is
72/(2π) ≈ 11.4591559026 cm. - The inner cut radius is
11.4591559026 − 1 ≈ 10.4591559026 cm. - The intended finished hem radius is
11.4591559026 + 55 ≈ 66.4591559026 cm. - The outer cut radius is
66.4591559026 + 1.5 ≈ 67.9591559026 cm. - The enclosing unfolded square side is approximately 135.918311805 cm.
The radial cut thickness is 55 + 1 + 1.5 = 57.5 cm. Notice that the waist allowance makes the cut hole smaller; it does not make the finished panel 1 cm shorter. The flat cut-panel area is about 14,165.6076 cm², which is an area rather than fabric yardage.
Change only the waist allowance
Keep that opening, length and hem allowance, but change the waist allowance from 1 to 1.5 cm. The inner cut radius becomes about 9.95915590262 cm. The stitched opening radius, finished hem radius and outer cut radius stay the same. The ring contains more fabric near the opening; its enclosing square does not grow.
A second set of chosen dimensions
With opening 100, length 40, waist allowance 1.25 and hem allowance 2, the stitched opening radius is about 15.9154943092 cm. The cut opening radius is about 14.6654943092 cm; the outer cut radius is about 57.9154943092 cm. The square side is about 115.830988618 cm. The 43.25 cm cut thickness equals 40 + 1.25 + 2.
Zero allowances show the underlying geometry
Choose opening 20, length 5 and both allowances 0. The opening cut edge and stitched opening share radius 3.18309886184 cm. The finished hem and outer cut edge share radius 8.18309886184 cm. The enclosing square is about 16.3661977237 cm on a side. Coincident lines in the diagram are expected when an allowance is zero.
An allowance can consume the opening
Opening 6 cm has seamline radius about 0.95493 cm. An inward waist allowance of 1 cm would leave a negative cut radius, so the input is rejected. The tool does not silently replace the cut hole with zero or invent a different construction. Review the chosen opening and allowance together.
A very small positive radius is not rounded to zero
Opening 6.284 cm with a 1 cm inward allowance leaves a small positive radius, around 0.0001297 cm. The display preserves a nonzero approximation instead of showing 0. That mathematical result is not a claim that such an opening is practical to mark or sew. The screen diagram may not visually resolve it.
Before cutting
Review your garment construction separately: the chosen opening, how the garment is put on, fabric stretch, grain and working clearance all matter. The square is only the geometric envelope for one unbroken ring. For a wearable result, use a suitable construction plan and check a paper draft or sample rather than treating these examples as a fitted pattern.