Calculation method

Canonical unit

Every length is converted to millimeters as the canonical unit before calculation. Inches use the exact definition 1 inch = 25.4 millimeters. Display conversion happens at the input and result boundaries so intermediate display rounding does not change geometry.

Formulas and validation

Inputs must be finite and dimensions that control geometry must be positive. Zero is accepted only for fields such as optional edge allowance. Whole-piece and panel counts must be positive integers. Errors point to the named form field.

Layout heuristic

Rectangular pieces use a deterministic shelf heuristic with stable sorting and explicit rotation gating. It produces a repeatable recommended layout and does not promise the shortest arrangement among every mathematically possible packing. Small fixtures are compared with bounded exhaustive checks without extending that conclusion to larger layouts.

Purchase policy

Geometry and pattern repeat are calculated first. Shrinkage is reversed by division, explicit waste is multiplied afterward, and the result is rounded upward to the selected purchase increment. The site never inserts a hidden waste or shrinkage percentage.

Scope

The calculations are educational planning models. They do not inspect fabric, certify fit, recommend structural hardware, or replace a commercial pattern. Written dimensions and a physical before-cutting check control over a scaled diagram.