ISO B5 versus JIS B5: the label does not fix the dimensions
Separate 176 ×250 mm from 182 ×257 mm before matching a notebook, cover or printable.
A B5 label is incomplete without the size family. ISO B5 is 176 ×250 mm. JIS B5 is 182 ×257 mm. JIS B5 is 6 mm wider and 7 mm taller. Ask for the actual dimensions and whether they describe the sheet, notebook cover or usable sleeve interior before choosing a replacement.
Keep the family beside the number
| Family | B5 | B6 |
|---|---|---|
| ISO B | 176 ×250 mm | 125 ×176 mm |
| JIS B | 182 ×257 mm | 128 ×182 mm |
These are reference sheet sizes, not a promise about every product sold as B5. A cover can extend beyond the paper; a manufacturer may use another named or proprietary format. Keep the published millimeters when a listing omits the family.
The mismatch is more than a rounding choice
The ISO B5 rectangle has 44,000mm² of area. JIS B5 has 46,774mm². The 2,774mm² difference is about 6.305% of the ISO rectangle's area. This original calculation says nothing about writing quality, page count or which notebook is better. It explains why a nominally matching cover or template may not match.
Two sheets can also share one edge and still have different shapes. Check both dimensions rather than deciding from a diagonal or a single B5 word.
Resolve a listing before buying another cover
- Copy the listed width and height. Retain units. If dimensions are absent, ask the seller rather than filling them in from a generic chart.
- Identify what was measured. Page size, closed cover size and a sleeve's usable interior answer different questions.
- Compare named families. Match dimensions to the ISO/JIS rows in the paper atlas. A close match is a clue, not proof of a manufacturer's designation.
- Measure your item. For a cover or pouch, include thickness and the actual opening. Use the three-axis numerical checker only when the relevant interior dimensions are known.
What to watch out for
- Using paper as the cover measurement. Reference dimensions cannot establish the exterior of a bound notebook.
- Calling a close fit guaranteed. Binding, corners, seams and insertion paths are not represented by two sheet dimensions.
- Replacing an exact value with rounded inches. Keep millimeters for the comparison; decimal inches in our atlas are derived display values.
- Treating a printer label as universal. A device or print service can offer one B family, another, or a custom size. Confirm the actual published dimensions for the selected option.
Choose the format for the job
The notebook-size guide handles desk and bag use. This page only resolves the B-family label. For a printable template, compare its actual page dimensions and use the physical-size print check rather than trusting the displayed zoom.
Sources and evidence
Mojoprint lists ISO/DIN B5 and B6 separately from JIS B5 and B6. Microsoft also lists 176 ×250 mm for B5, 182 ×257 mm for JIS B5 and 128 ×182 mm for JIS B6. These are published references, not measurements of your notebook or proof of printer compatibility. NIST SP 1038: exact unit conversion (PDF) is the separate reference for converting units, not a paper-size standard. Sources read November 8, 2026.
Common checks
Does B5 always mean 176 ×250 mm?
No. ISO B5 uses those nominal dimensions, while JIS B5 is 182 ×257 mm. A product listing still needs its own measured page or cover dimensions.
Can the B5 sheet chart prove a sleeve fits my notebook?
No. Sheet size does not establish cover dimensions, thickness, sleeve interior or insertion clearance.
Unpublished review draft. Sources last read November 8, 2026. Send a correction.