Hobonichi Size and Cover Compatibility

Hobonichi uses familiar A6 and A5 labels, but cover compatibility follows product families rather than paper labels alone. The standard map is simple once books with attached covers and multi-year formats are separated from the reusable-cover system.

This guide records the current 2026 official lineup. It does not assume that a third-party cover fits, and it does not extend a compatibility statement from one product family to another.

Core compatibility map

The current official A6 cover specification explicitly names Planner, Original, Original Avec, and Day-Free as compatible. The current lineup similarly states that Day-Free can use the standard A6 Original or A5 Cousin covers. These manufacturer statements are the foundation of the map.

Original, Planner, and Avec share the A6 cover family

Original is Hobonichi’s standard A6 page-per-day book. The current official specification lists a book size of 105 × 148 mm. Planner is also an A6 page-per-day book, with an English layout. Original Avec divides the year between two books.

Standard A6 Original covers are designed around this family. That does not mean every configuration feels identical inside the cover. The full-year books and split-year Avec have different thicknesses, and inserted papers or accessories change the stack. The compatibility statement means the books belong to the cover family; it does not guarantee the same fullness.

Language does not normally create a new physical cover family for the standard A6 book. A Japanese Original and English Original can share dimensions while presenting different calendar and supplemental content. Confirm the current product page if a special edition changes construction.

Cousin and Cousin Avec use the A5 family

Cousin moves the page footprint to A5, 148 × 210 mm, and adds a weekly section to the page-per-day structure. The current type guide lists the full-year Cousin as thicker and heavier than its A6 counterpart. Cousin Avec splits the year into two A5 books.

A5 Cousin covers are the relevant reusable family. An A6 Original cover cannot be scaled by intuition; it is a separate product. Conversely, a generic A5 book may share the page footprint but lack an official fit statement for Hobonichi’s closure, pockets, and expected thickness.

When comparing a third-party cover, record its stated inner dimensions and whether the seller names the current Cousin. “Fits A5” is weaker than “fits Hobonichi Cousin 2026,” and neither is evidence that Bungu Atlas has physically tested the combination.

Day-Free crosses into the standard cover families

Day-Free combines dated monthly calendars with undated graph-paper notebook pages. It is offered in A6 and A5. The current lineup says the A6 Day-Free can use standard Original covers and the A5 Day-Free can use standard Cousin covers, alongside Day-Free-specific cover options.

This is an explicit manufacturer bridge between product formats. It is stronger than a dimensional inference. The book is thinner than a full page-per-day annual book, so the finished feel inside a cover can differ even though compatibility is established.

Do not confuse Day-Free’s undated notes with an undated version of every Hobonichi layout. It lacks the full daily sequence and should be chosen for its page structure, not only its cover fit.

HON has an attached hardcover

HON is a page-per-day Techo with a hardcover already attached. The current official chart lists A6 HON at approximately 110 × 156 mm and A5 HON at approximately 152 × 214 mm—larger than the underlying A6 and A5 page footprints.

That attached cover is the reason HON must be treated separately. A standard Original or Cousin cover is designed around a flexible book block, not automatically around a finished hardcover. Hobonichi offers HON-specific protective accessories and product-level compatibility notes.

The correct shopping question is not “Is HON A6?” It is “Does this accessory explicitly fit the A6 HON, including its attached cover?”

Weeks and Weeks Mega are wallet size

Weeks is 95 × 186 mm in the current chart, a tall wallet-size format with weekly horizontal pages and memo space. Weeks Mega keeps the general footprint while adding nearly three times the blank graph-paper pages according to the official comparison, increasing thickness.

Weeks products have their own clear covers and cases. Do not map them to A6 because the writing area appears compact. The proportions, spine, and cover construction differ.

A listing that says “Weeks compatible” may still distinguish standard Weeks, Mega, Sneaker, or special cover materials. Use the current accessory page for the exact book edition.

5-Year Techo uses dedicated covers

The 5-Year Techo displays the same date across five consecutive years. Although its models are described with A6 and A5 size classes, the multi-year book block is not the ordinary one-year Original or Cousin.

The current lineup presents dedicated 5-Year Techo covers. That dedicated label should control the purchase. A standard A6 or A5 cover statement should not be extended to a much thicker five-year volume without explicit support.

US sales configuration can affect the bundle

Hobonichi’s 2026 shopping instructions describe special sales arrangements for products shipped to the United States. For specified cover families, covers may be offered with eligible books rather than on their own. The compatible book list shown in that sales flow is also useful evidence, but availability and bundle rules can change by year.

Separate three questions:

1. Is the book physically compatible with the cover family?
2. Is that exact cover currently sold to the United States?
3. Can it be purchased alone, or only with a listed book?

A “yes” to the first does not guarantee a “yes” to the next two.

Safe purchase workflow

1. Identify the exact book: Original, Planner, Avec, Cousin, Day-Free, HON, Weeks, or 5-Year.
2. Record A6, A5, or wallet size, but keep the product family beside it.
3. Open the current official cover page and read its “Compatible Techo Books” list.
4. Check the current US shopping instructions for bundle and shipping limits.
5. Treat third-party compatibility as unverified unless that seller names the exact current book.

The result is conservative by design. A cover is cheaper than an international return, but a compatibility assumption can make both expensive.