Transitional Paper Sizes

The transitional paper size formats consist primarily of two series - the PA Series and the F Series. The PA Series was proposed in 1975 to be included in the ISO 216 standard, but was ultimately rejected in favor of keeping the number of standardized formats to a minimum. However, the PA Series is still commonly used today, especially the PA4 size which has dimensions of 210mm x 280mm (matching the width of ISO A4 and the height of Canadian P4). This makes PA4 well-suited for international magazines and presentation slides. More broadly, the PA Series formats have dimensions based on halving or quartering the next larger size in the series. The end result is a range of rectangular formats with aspect ratios of 1:√2.

The F Series formats are commonly used in Southeast Asia. The F4 size is notable, with dimensions of 330mm x 210mm - the longer side matches British Foolscap while the shorter side matches ISO A4. The F Series dimensions do not follow the logic of the PA Series; instead the sizes have an aspect ratio closer to 4:3. The F Series is sometimes known as "metric foolscap" given its roots in the British paper system. Both the PA and F transitional series serve niche applications, filling gaps left by the limited number of ISO 216 standardized sizes. Their adoption demonstrates the utility of these in-between formats.