D5

The D5 sheet dimensions of 136 mm by 192 mm represent the smallest landscape format in the DIN 476 German paper size system. With an area of 0.026 square meters, the size falls between ISO A6 and A5 dimensions. In particular, D5's elongated proportions nearing a width-to-height ratio of 1.27 suit technical drawings requiring more lateral space than A5 offers. The UK "Post Octavo" sheets closely match D5 as well.

Likely adapted from prior German and Central European graphic formats, the diminutive D5 dimensions meet specialized diagramming needs in between standardized sizes. The width extends segmentation that better fits formatting technical specifications and landscape data presentations. However, just as C series envelopes and B series intermediate sizes never gained adoption over ISO 216, the D5 sheet saw declining post-war usage in favor of standardized A dimensions. Nonetheless, DIN 476's intent to provide flexible sizing lives on through the D series complementing common A, B, and C sizes even if obsolete today.