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9×12 vs 10×13 Catalog Envelopes: 9×12 Leaves 0.5 in, 10×13 Leaves 1 in Around a Letter Sheet
The two catalog envelopes compared
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Industry standard
9×12 catalog envelope
9 × 12 in (228.6 × 304.8 mm)
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Industry standard
10×13 catalog envelope
10 × 13 in (254 × 330.2 mm)
The short answer
- 9×129 × 12 in (228.6 × 304.8 mm) — Letter fits with 0.25 in each side, 0.5 in each end
- 10×1310 × 13 in (254 × 330.2 mm) — Letter fits with 0.75 in each side, 1 in each end
- Difference10×13 is 1 in wider, 1 in taller, and gives 3× the clearance around a Letter sheet
See the sizes in AR (shown as boxes)
The two sizes as boxes at their published dimensions
Preparing 3D…
1 9×122 10×13
On a phone, the "View in your room (AR)" button places the boxes in your room. The boxes are locked to the published dimensions and cannot be resized. They show size only and are not 3D replicas of the products.
Drawn to the same scale
Dimensions side by side
| Item | 9×12 catalog | 10×13 catalog | Difference |
|---|---|---|---|
| Width | 9 in (228.6 mm) | 10 in (254 mm) | 10×13 is 1 in (25.4 mm) wider |
| Height | 12 in (304.8 mm) | 13 in (330.2 mm) | 10×13 is 1 in (25.4 mm) taller |
| Letter clearance — width | 0.5 in total (0.25 in each side) | 1.5 in total (0.75 in each side) | 10×13 has 1 in (25.4 mm) more room |
| Letter clearance — height | 1 in total (0.5 in each end) | 2 in total (1 in each end) | 10×13 has 1 in (25.4 mm) more room |
Millimeter values converted at 1 in = 25.4 mm. Dimensions are nominal; actual envelopes vary slightly by manufacturer and paper stock. US Letter is 8.5×11 in (215.9×279.4 mm) per ASME Y14.1.
What the numbers mean
Both envelopes hold a US Letter sheet (8.5×11 in) flat, with no folding. That is the defining feature of the catalog format: the flap is on the short edge, so the full 8.5 in width slides in lengthwise.
The 9×12 gives 0.25 in (6.4 mm) on each side and 0.5 in (12.7 mm) at each end. That is enough for a single sheet or a small stack with a light cardboard back.
The 10×13 gives 0.75 in (19.1 mm) on each side and 1 in (25.4 mm) at each end. The extra room is useful for thick packs, tabbed dividers, or content with edge annotations that come close to the 8.5 in margin.
Neither envelope is a USPS flat-rate product. Both mail as First-Class or Priority flats. The USPS defines a flat as 6.125 to 15 in long and 5 to 12 in wide; both sizes qualify. The 10×13 is lighter on postage when the content is under 1 oz, but the extra inch of paper adds a few grams to the starting weight.
Product links
FAQ
Will a US Letter sheet fit flat in a 9×12 catalog envelope?
Yes. A US Letter sheet (8.5×11 in / 215.9×279.4 mm) fits flat in a 9×12 catalog envelope (9×12 in / 228.6×304.8 mm) with 0.25 in (6.4 mm) of clearance on each side and 0.5 in (12.7 mm) of clearance at each end.
What is the difference between a 9×12 and a 10×13 catalog envelope?
A 9×12 catalog envelope measures 9×12 in (228.6×304.8 mm). A 10×13 measures 10×13 in (254×330.2 mm). The 10×13 is 1 in (25.4 mm) wider and 1 in (25.4 mm) taller. When inserting a US Letter sheet flat, the 9×12 leaves 0.5 in total clearance in width and 1 in total in height; the 10×13 leaves 1.5 in total in width and 2 in total in height.
What is a catalog envelope used for?
Catalog envelopes (also called open-end envelopes) have a flap on the short edge, so documents slide in flat without folding. They are used for multi-page documents, catalogs, reports, legal filings, and anything too thick or wide to fold into a #10.
Can a Letter sheet fit flat in a 10×13 catalog envelope?
Yes. A US Letter sheet (8.5×11 in / 215.9×279.4 mm) fits flat in a 10×13 catalog envelope (10×13 in / 254×330.2 mm) with 0.75 in (19.1 mm) of clearance on each side and 1 in (25.4 mm) of clearance at each end. The extra room makes it easier to insert and remove thick stacks.
See also: US Envelope Sizes: #10, #9, #6¾, A2, A7 — the folded-letter and greeting-card sizes. A4 vs Letter — the paper that goes inside. ANSI Paper Sizes A–E — how Letter fits in the full ANSI series.
Sources
- 9×12 and 10×13 catalog envelope dimensions: envelopes.com Envelope Size Guide, envelopes.com/pages/envelope-size-guide, checked 2026-10-03; businessenvelopes.com product pages, businessenvelopes.com, checked 2026-10-03. Nominal names equal the stated dimensions: 9×12 = 9×12 in, 10×13 = 10×13 in.
- US Letter dimensions: ASME Y14.1, 8.5×11 in (215.9×279.4 mm).
- USPS flat mail size standards: USPS Domestic Mail Manual Section 101, pe.usps.com/text/dmm300/101.htm. Flat: 6.125–15 in long, 5–12 in wide, up to 3/4 in thick.