Japanese Notebook Size Chart in Inches and Millimeters

Japanese notebook names mix international paper standards, Japanese book conventions, and manufacturer-specific systems. A6 and A5 are ISO page sizes. B6 Slim is a product format rather than one universal international rectangle. Weeks, Regular, and Passport are names inside particular planner or refill systems.

The safest shopping coordinate is always width × height in millimeters, followed by the product family. Inches are useful for visualizing the object in the United States, but rounded inch values should not be used to prove cover, ring, or refill compatibility.

Quick size chart

Inch values are rounded to two decimal places from the official metric figures. A seller may round differently. A 4.1-inch listing and a 4.13-inch conversion can describe the same 105 mm dimension.

Why millimeters should remain the source value

One inch equals exactly 25.4 millimeters. Conversion itself is simple, but shopping titles often round to one decimal place. That can erase a meaningful difference.

For example, 105 mm converts to about 4.13 inches and 110 mm converts to about 4.33 inches. Both may be described casually as “about four inches wide,” yet the five-millimeter gap is enough to create overhang or looseness in a fitted accessory.

Keep the manufacturer’s millimeter specification in notes and use inches only as a second display unit. Do not convert a rounded inch figure back into millimeters and treat the result as an official measurement.

A7, A6, and A5 follow the ISO A-series

The A-series preserves the same proportions as each sheet is divided in half. A5 measures 148 × 210 mm. Cutting it across the long side produces two A6 sheets of 105 × 148 mm. Repeating the division produces A7 at 74 × 105 mm.

That relationship explains why A5 has twice the page area of A6 even though neither edge simply doubles. It also explains why an A5 sheet can be folded into A6 sections without changing the overall proportions.

The size standard describes a page footprint, not a finished notebook exterior. Covers, boards, rings, tabs, binding cloth, and rounded corners can extend beyond the sheet.

B6 Slim is not one universal B6 promise

Japanese notebook catalogs use B labels in several ways. MD Notebook B6 Slim is officially listed at 105 × 175 mm. Other products described as B6, Semi-B6, or B6 Slim can use different dimensions.

The word “Slim” signals that at least one dimension has been changed from a broader B6 reference, but it does not define the amount. A fitted cover should name the exact notebook or state internal dimensions compatible with 105 × 175 mm plus the book’s thickness.

Treat B6 titles as a prompt to find millimeters, not as the final compatibility answer.

Hobonichi uses both standards and proprietary formats

Hobonichi Original uses A6, 105 × 148 mm. Cousin uses A5, 148 × 210 mm. Those page footprints align with the ISO names, while cover compatibility remains tied to Hobonichi product families and book thickness.

Weeks is different. Its 95 × 186 mm wallet-size format is narrower than A6 and taller than A6. A Weeks accessory is therefore not an A6 accessory, even though both planners are designed to be carried.

HON adds a hardcover to A6- or A5-class pages and has larger finished dimensions. A size chart should distinguish the book block from the finished hardcover before comparing cases.

TRAVELER’S Regular is A5-height, not A5

The Regular refill is 110 × 210 mm. It shares A5’s 210 mm height but is 38 mm narrower. The common phrase “narrow A5” can help someone picture the shape, but it is not the system name and should not be used to select a refill.

Passport refills are 89 × 124 mm. They are smaller than A6 in both dimensions and belong to the Passport elastic-cover system. A generic passport-themed notebook can use a different size.

For both systems, the leather cover is larger than the refill. Compare refills with refills and covers with covers.

Kokuyo binder dimensions describe more than paper

The current Kokuyo Campus four-ring Binder Notebook examples list A5 and B5 products with exterior dimensions larger than the loose-leaf sheets they hold. The A5 binder exterior is about 162 × 217 mm, while A5 paper remains 148 × 210 mm. The B5 binder exterior is about 195 × 264 mm around B5 loose leaf.

Hole count and mechanism matter as much as page size. A four-ring binder can be designed to accept selected holes in conventional multi-hole loose leaf, but “A5” alone does not state the ring layout.

How to measure a notebook listing

Record the values in this order:

1. width, measured across the closed front;
2. height, measured along the spine direction;
3. thickness of the bare book;
4. finished width and thickness with the intended cover;
5. rings, holes, elastic bands, or other system constraints.

If a listing reverses height and width, compare the rectangle rather than the order of the words. A portrait A5 book may be written as 210 × 148 mm even though this atlas uses width × height, 148 × 210 mm.

Printable conversion rule

To convert millimeters to inches, divide by 25.4. To convert inches to millimeters, multiply by 25.4. Keep at least two decimal places while calculating, then label the final inch figure as approximate.

For purchase decisions, return to the official metric value. The conversion helps a US shopper imagine the notebook beside a familiar object; it does not turn a proprietary refill system into a standard paper size.

Check print scale before using a paper template

A printed rectangle is useful only when the printer preserves scale. Browser and PDF dialogs can silently select “fit to page,” shrinking or enlarging the template to match printable margins.

Include a control line with a known length, such as 100 mm, and measure it with a physical ruler after printing. If that line is not exactly 100 mm, do not use the template to judge a cover. Select 100 percent or actual-size printing and repeat the check.

Even a correctly printed page template proves only width and height. Folded signatures, boards, rings, and a growing stack of pasted material add a third dimension. For a close-fitting cover, construct a paper block at the stated thickness or compare the exact finished-book specification.

Screens are less reliable than printed scale because browser zoom, operating-system scaling, pixel density, and viewport size all change the displayed rectangle. The comparison tool on this site preserves relative proportions, not life-size output.