The difference is directional
DL is about 5.23 mm wider, while #10 is about 21.3 mm longer. Neither outline contains the other in the same orientation, so “closest equivalent” should not be read as interchangeable.
Envelope comparison
DL vs #10 envelope
DL and #10 serve a similar correspondence role but are not the same size. DL is 110 × 220 mm; #10 is 4 1/8 × 9 1/2 inches (104.78 × 241.3 mm).
Nominal size reference
Compare the recorded formats
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 |
|---|---|---|---|---|
| DLInternational | 110 × 220 mm | 4.331 × 8.661 in | Envelope Manufacturers Association ↗27 August 2026 | A4 paper folded into thirds |
| #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 |
Original comparison
See the dimensional difference
The outlines use nominal face dimensions from the canonical records. They do not imply identical seams, flaps, usable capacity or manufacturing tolerance.
Match the paper system and fold
DL commonly accompanies A4 folded into thirds. #10 commonly accompanies US Letter tri-folded. Use the actual finished insert when crossing between systems.
Choose by task, not visual similarity
Use DL for an A4-based workflow and #10 for a US Letter-based workflow unless a measured insert or supplier specification points elsewhere.
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.