DL stands for dimension lengthwise and is a common size for envelopes and promotional materials such as brochures and flyers. The C Series in the ISO 269 standard defines DL size to be 100mm × 210mm, which is also exactly a third the size of an A4.
Usually DL size stock will be used for envelopes, brochures, flyers, leaflets, cards and invitations.
In the ISO paper size system, the height-to-width ratio of all pages is the square root of two. In other words, the width and the height of a page relate to each other like the side and the diagonal of a square. This aspect ratio is especially convenient for a paper size. If you put two such pages next to each other, or equivalently cut one parallel to its shorter side into two equal pieces, then the resulting page will have again the same width/height ratio.
- DL is a third the size of A4.
- DL is one-sixth the size of A3, and one-twelth the size of A2.
- Thirty-two DLs will make up an A1, and sixty-four to make up an A0.