B paper sizes: ISO B and Japanese JIS B

ISO B series size chart

Sizes are given as width by height of an upright sheet.

Japanese JIS B series size chart

Japan uses the same A series as the rest of the world but keeps its own, slightly larger B series.

How to use the charts

1. Find out which market the product was made for. Paper products made for Japan generally follow the Japanese standard; elsewhere B sizes generally mean ISO B.
2. Look for millimetre dimensions in the product description and compare them with both charts.
3. If only the name is given, for example B5, ask the seller or assume the series of the country of origin.

B sizes sit between the A sizes. ISO B5 is larger than A5 and smaller than A4.

How the sizes are derived

ISO 216 defines B0 with a short side of exactly one metre and the same side ratio as the A series, 1 to the square root of 2. B0 is therefore 1000 mm by 1414 mm. Each next size is the previous one cut in half across its long side, rounded down to the whole millimetre.

Seen another way, each ISO B size is the geometric mean of two neighbouring A sizes: B1 lies between A0 and A1.

The Japanese series starts from JIS B0, 1030 mm by 1456 mm, and is halved in the same way. JIS B0 is described as having an area of 1.5 square metres, which makes every JIS B sheet about 6 percent larger in area than the ISO sheet with the same name.

Both charts on this page are calculated from the B0 size and were then compared with published tables.

Worked example: a cover for a B5 notebook

You have a notebook from Japan labelled B5 and want a cover sold in Europe as B5. The notebook is JIS B5: 182 mm by 257 mm. The cover is made for ISO B5: 176 mm by 250 mm.

The notebook is 6 mm wider and 7 mm taller than the sheet the cover was designed for. Unless the cover has that much spare room, it will not fit. Look for a cover that states 182 by 257 mm or names JIS B5.

Common mistakes

• Assuming B5 means the same everywhere. It does not.
• Choosing B4 in a print dialog without checking which one. The paper size list of Windows contains both B4 (ISO) and B4 (JIS).
• Mixing up B sizes and C sizes. C sizes are envelopes.
• Reading the inch values as exact. They are rounded conversions.

• A series paper sizes
• C series envelope sizes

Sources and checks

The values in the chart are calculated from the definitions in the sources below. They are not copied from another chart. Last checked against the sources on September 28, 2026.

ISO B sizes are calculated from B0 (1000 mm by 1414 mm) by halving and rounding down; the result was compared with Table 2 of the ISO 216:2007 preview and matches.

JIS B sizes are calculated the same way from JIS B0 (1030 mm by 1456 mm); the result was compared with the JIS B values in PWG 5101.1 and matches for B0 to B10.

That JIS B0 has an area of 1.5 square metres is taken from a secondary source; the text of the Japanese standard was not read.

• ISO 216:2007, Writing paper and certain classes of printed matter: trimmed sizes, A and B series (ISO catalogue entry)

Used for: Title, edition and status of the standard that defines the A and B series.

• ISO 216:2007 preview, clauses 1 to 6 (iTeh Standards sample)

Used for: Halving principle, side ratio of 1 to the square root of 2, A0 area of one square metre, B sizes as geometric means, and the millimetre values of A0 to A10 and B0 to B10 used to check the calculation.

• JIS P 0138:1998, trimmed sizes of paper, A and B series (Japanese Standards Association catalogue entry)

Used for: Existence, title and status of the Japanese standard that keeps its own B series.

• PWG 5101.1-2023, Media Standardized Names 2.1 (IEEE-ISTO Printer Working Group)

Used for: Dimensions of North American, engineering, architectural, ISO C, envelope and JIS B sizes as used by printers and print software.

• Markus Kuhn, International standard paper sizes (University of Cambridge Computer Laboratory)

Used for: Rounding down to the millimetre after each halving, the tolerances of ISO 216, the C series as geometric mean of A and B, and which sheet fits which envelope.