The ISO family of paper is commonly used in Europe. It uses a single aspect ratio for all sizes in its range. Most paper is in the A Series. It is defined by ISO 216.

A0 is one square meter, with the sides forming a ratio of 1:14142 (1:√2, or one to the square root of two). Each smaller size of paper is half of its predecessor, divided on the longer edge, retaining this ratio. The short side of one size becomes the long size of the next smaller one. This allows for consistent steps up and down. Enlarging or reducing on a copier makes for consistent steps with no blank space.

While it’s less common in the United States, I prefer it, if only for the geeky logic behind it. I also find that ISO paper sizes are what is typical for the most fountain pen friendly paper.

Size | Inches | Millimeters | Notes |
---|---|---|---|

A0 | 33.125 x 46.8125 | 841 x 1188 | The origin. One square meter |

A1 | 23.375 x 33.125 | 594 x 841 | |

A2 | 16.5 x 23.375 | 420 x 594 | |

A3 | 11.75 x 16.5 | 297 x 420 | Close match to “tabloid” paper |

A4 | 8.25 x 11.75 | 210 x 297 | Close analog to “letter.” A bit narrower and taller. |

A5 | 5.875 x 8.25 | 148 x 210 | “Junior” size paper. Most journals are this size. |

A6 | 4.125 x 5.875 | 105 x 148 | Good pocket notebook size |

A7 | 2.9375 x 4.125 | 74 x 105 | A good, if smaller, notebook size |

A8 | 2.0625 x 2.9375 | 52 x 74 | ISO-sized business card |

Hypothetically, you can keep halving the paper until you reach some atomic size.

The B series is used to fill some gaps in the A series. It uses the same ratio, but based on geometric mean of two a sizes. It has the same It’s used to fill gaps between sizes of A. It’s less common, but does come up for some stationary.

Size | Inches | Millimeters | Notes |
---|---|---|---|

B0 | 39.4 x 55.7 | 1000 x 1414 | |

B1 | 27.8 x 39.4 | 707 x 1000 | |

B2 | 19.7 x 27.8 | 500 x 707 | |

B3 | 13.9 x 19.7 | 353 x 500 | |

B4 | 9.8 x 13.9 | 250 x 353 | |

B5 | 6.9 x 9.8 | 176 x 250 | Books, some journals |

B6 | 4.9 x 6.9 | 125 x 176 | Books, some journals |

B7 | 3.5 x 4.9 | 88 x 125 | Passports ISO 7810, ID-3 |

B8 | 2.4 x 3.5 | 62 x 88 | Playing cards |

B9 | 1.7 x 2.4 | 44 x 62 | |

B10 | 1.2 x 1.7 | 31 x 44 |

The C series is the geometric mean between the A and B series of the same number. It is used for envelopes. C4 is a *bit* larger than A4, and can fit a sheet unfolded. A C5 envelope can hold an A4 sheet folded in half, and so forth.

Size | Inches | Millimeters | Notes |
---|---|---|---|

C0 | 36.1 x 5.11 | 917 x 129.7 | |

C1 | 25.51 x 36.1 | 648 x 917 | |

C2 | 18.03 x 25.51 | 458 x 648 | |

C3 | 12.76 x 18.03 | 324 x 458 | |

C4 | 9.02 x 12.76 | 229 x 324 | |

C5 | 6.42 x 9.02 | 163 x 229 | |

C6 | 4.49 x 6.38 | 114 x 162 | |

C7 | 3.19 x 4.49 | 81 x 114 | |

C8 | 2.24 x 3.19 | 57 x 81 | |

C9 | 1.57 x 2.24 | 40 x 57 | |

C10 | 1.1 x 1.57 | 28 x 40 |

Unlike the ISO standards, the North American sizes have no real rhyme or reason. Rather, they are based on a quixotic choice made by paper makers a long time ago. Generally, you will encounter Letter size, with most “journals,” like Moleskine are roughly half-letter sized.

Size | Inches | Millimeters | Notes |
---|---|---|---|

Letter | 8.5 x 11. | 215.9 x 279.4 | |

Legal | 8.5 x 14. | 215.9 x 355.6 | |

Tabloid/Ledger | 11. x 17. | 279.4 x 431.8 | |

Junior Legal | 5. x 8. | 127. x 23.2 | |

Half-Letter | 5.5 x 8.5 | 139.7 x 215.9 | |

Government Letter | 8 x 10 | 203 x 254 | Perscribed by Hoover; Reagan went back to “normal” letter. |

Executive | 7.25 x 10.5 | 184.15 x 266.7 | |

Business Card | 3.5 x 2.0 | 89 x 51 |

This covered the most common, general purpose paper sizes. There are some that are unique to different countries, proprietary to a specific manufacturer, or some other custom application.

Size | Inches | Millimeters | Notes | |
---|---|---|---|---|

Field Notes | 3.5 x 5.5 | 89 x 140 | Original "Kraft" pocket-sized notebook | |

"Sawed Off A4" | 8.25 x 11 | 210 x 279.4 | My custom size--an A4 sheet cut to US Letter height, to fit in US binders. | |

B6 Slim | 4.2 x 6.9 | 106 x 174 | I've seen this used in some planners, such as the Kokuyo Jibun Techo, as well as other notebooks. | |

A5 Slim | 5.4 x 8.6 | 136 x 218 | Anohter "slim" offered for the Kokuyo Jibun Techo. I haven't seen it myself. |

Last updated on January 7, 2024.

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