Paper & card guide
A #10 is the familiar choice for US Letter paper tri-folded. A 9 × 12 booklet or catalog envelope provides room for the sheet flat.
Nominal size reference
Every table uses nominal exterior width × height. International sizes lead with millimetres; US sizes lead with conventional fractional inches.
| Format | Native size (width × height) | Converted size (width × height) | Source checked | Context |
|---|---|---|---|---|
| #10US commercial | 4 1/8 × 9 1/2 in4.125 × 9.5 in decimal | 104.77 × 241.3 mm | Neenah Paper ↗27 August 2026 | US Letter paper folded into thirds |
| 9 × 12 bookletUS booklet | 9 × 12 in9 × 12 in decimal | 228.6 × 304.8 mm | Neenah Paper ↗27 August 2026 | US Letter paper flat with generous nominal space |
| 9 × 12 catalogUS catalog | 9 × 12 in9 × 12 in decimal | 228.6 × 304.8 mm | Neenah Paper ↗27 August 2026 | US Letter paper flat with generous nominal space |
US Letter is 8 1/2 × 11 inches. A tri-fold is approximately 3 2/3 × 8 1/2 inches before fold thickness and variation. A half-fold is approximately 5 1/2 × 8 1/2 inches.
A roll fold and a Z-fold create different layer stacks even when the outer rectangle is similar. Measure a representative folded set when several sheets are involved.
Nominal envelope dimensions describe the exterior format, not guaranteed usable internal space. Seams, lining, stock thickness, multiple pieces and manufacturing tolerances reduce practical room; sample before a bulk order or print run.
Current postal eligibility depends on more than the nominal envelope name.