Methodology
Matching uses exact millimetre values internally, converts inches at 25.4 mm per inch, tests both orientations and applies the chosen clearance on every edge.
Every EnvelopeLogic answer, table heading, diagram and calculation presents the nominal exterior face as width × height. For the supported records, width is the shorter face dimension and height is the longer face dimension; a supplier may rotate the product or list height before width. Open side means the opening follows the longer edge. Open end means it follows the shorter edge.
Calculations use exact millimetre values internally and exactly 25.4 mm per inch. International formats show their exact integer millimetres first and converted inches to three decimal places, with trailing zeroes removed. US formats show conventional fractional inches first, then exact decimal inches to no more than three decimal places and metric conversions to no more than two decimal places. Rounding is display-only and never changes matcher arithmetic.
For each dimension: remaining = nominal envelope dimension − insert dimension − (2 × per-edge clearance). “Remaining” always means the total unused width or total unused height after the chosen clearance has already been reserved on both edges.
A candidate is recommended when both remaining dimensions are at least 2 mm. It is borderline when the arithmetic passes but either remaining dimension is below 2 mm. It does not fit when either remaining dimension is negative. This documented 2 mm buffer is a cautious working rule, not a manufacturing or postal standard.
Straight and 90-degree orientations are tested. Rotated-only results are labelled. Fold presets use the named finished rectangle; they do not model thickness, fold quality, spring-back or several sheets.
Each canonical record includes the source publisher, title, link, exact fact supported, checked date, standards-status note and rights restriction.
EnvelopeLogic independently records the minimum factual dimensions and creates its own wording, calculations and diagrams. A source link is evidence for a stated fact, not permission to reproduce the source presentation.