Notebook Sizes: A4, A5, A6 and B5 Compared

"A5" and "B5" get thrown around constantly when people talk about notebooks, but most of us have only a rough sense of what those letters and numbers actually mean in the hand. Knowing the real dimensions and the difference between a couple of naming systems makes it much easier to pick a size that actually fits how you plan to use it.

The size chart

Why are there two different "B" sizes

The A-series (A4, A5, A6, A7) is consistent worldwide: it’s an international ISO standard with the same dimensions. The B-series, though, gets more interesting if you enjoy being confused in a stationery shop: ISO has its own B-series, but Japan uses a separate JIS (Japanese Industrial Standards) B-series with the same names (B5, B6) that actually describe slightly larger sheets.

The difference isn't too dramatic, though it is noticeable: a JIS B5 notebook is noticeably roomier than an ISO B5 one, even though both are labelled "B5." If you're comparing a notebook sold in Japan against one sold in Europe or the US, checking whether it's using ISO or JIS dimensions is worth the extra thirty seconds before you buy.

Page size isn't the same as the notebook you're holding

The dimensions above describe the page, not the notebook as a physical object. A bound notebook's outer cover is always a little larger than the paper inside it, to protect the edges and allow the cover to close flush. How much larger depends on the binding style: a notebook with a thick padded cover will add more to the overall footprint than one with a thin, flexible one.

This matters when you're fitting a notebook into something else, like a bag pocket. The page size tells you how much room you'll have to write; the cover dimensions tell you whether it'll actually fit where you want to put it. If you're shopping by dimensions alone, it's worth checking that a listing specifies which one it's quoting, though usually the page size is mentioned.

Comparing sizes for how you actually use a notebook

A4 vs. A5

A4 gives you a full page's worth of room; it is your typical office paper size, which suits detailed planning, sketching with space to spread out, or any notebook that mostly stays on a desk. A5 is roughly half an A4 sheet.

A4 notebook size is very common among students or those writing a lot daily and carrying a bag big enough to fit the laptop, which usually covers A4 size pretty well. A4 gives more than enough room for writing down big paragraphs of text, drawing schemes, or sketching ideas. 

A5 notebook is the size most people picture when they think "notebook." It is more than enough for comfortable daily writing, though if you prefer drawing a lot, you might find yourself fitting the last lines of the text at the bottom of the page a little too often for your liking.

A5 vs. A6

A6 is about half of A5 again. 

A6 fosters shorter lines, more abbreviations, and more page turns, which suits quick capture (a to-do list, a phone number, a fleeting thought) far better than sustained writing. A6 is also genuinely far more pocketable than any of the notebook sizes mentioned in this guide.

A5 vs. B5

B5 sits between A4 and A5: it is noticeably roomier than A5 without being as large as a full A4 page. If A5 ever feels slightly tight for how much you write per session (long meeting notes, detailed journaling, or maybe simply larger handwriting), B5 gives meaningful extra width and length, though it's a step up in bag space compared to A5.

Which size fits which situation

• Desk work, longhand and detailed planning: A4, or B5 if you want something a little more compact than full-size paper

• Meetings and everyday note-taking: A5 is the most common sweet spot; enough space to write properly, still easy to carry

• Quick capture and portability: A6, especially if it needs to fit in a pocket alongside pocket pens for a portable writing setup

• Longer personal writing, like journaling: A4, A5 or B5, depending on how much you tend to write per entry. See our guide on starting a writing journal for more on finding a comfortable rhythm

Worth remembering: size is a separate question from how paper actually performs under a fountain pen. A generously sized notebook can still bleed or feather if the paper itself isn't suited to it. That's a matter of choosing paper for fountain pens , not of dimensions.

A quick way to choose

• Do you mostly write at a desk, or on the move? Desk-bound leans A4/B5; portable leans A5/A6.

• How much do you tend to write per session? Short notes suit a smaller page; longer entries want more room per line.

• How big is your handwriting? Bigger letters or greater tilt might feel more natural on the larger page, and vice versa.

• Does it need to fit somewhere specific: a bag pocket, a drawer? Check cover dimensions, not just page size.

• If you're comparing a notebook labelled B5, confirm whether it's using ISO or JIS dimensions before assuming size from the label alone.