A3.1

The A3.1 is an elongated format defined in ISO 5457. It combines the 297 mm short side of an A3 sheet with the 841 mm long side of an A1 sheet. This results in the A3.1 having dimensions of 297 mm x 841 mm. With an aspect ratio of 2√2:1, the A3.1 has the unique property of being the same proportion as A3, just scaled up. The total surface area of an A3.1 sheet is 249,677 mm2 or 0.2497 m2.

The A3.1, introduced in ISO 5457 in 1999, aims to provide more flexibility while maintaining consistency with the width-to-length ratios of standard A-series sizes. The motivation was that some technical drawings and designs benefit from a particular elongated orientation on a longer sheet that preserves the original proportions. The A3.1 serves this need with its 841 mm elongated dimension compared to A3. The A3.1 has been adopted by ANSI/ASME Y14.1 for use in the United States alongside regular A3 and other A-series sizes. In summary, the elongated A3.1 format allows for narrow A3-ratio drawings on an extended sheet while keeping the familiar A-series proportions.