Key points
- A5 (148 by 210 mm) is the standard for a desk journal and the size with the most refills, covers and accessories. B6 (128 by 182 mm) is the bag size. A6 (105 by 148 mm) and 3.5 by 5.5 inch pocket notebooks are the jacket sizes.
- A refillable leather cover only saves money if its inserts are a standard size. Check the insert dimensions, not just the name, before buying a cover.
- Traveler's-style inserts are a tall narrow 110 by 210 mm and do not fit A5 covers, and A5 inserts do not fit traveler's covers. The two are the most common mismatch.
- Page count and paper weight set the thickness. A 200-page A5 in 90 gsm paper is roughly twice the thickness of the same notebook in 52 gsm.
Half the frustration with refillable notebooks comes from two systems using the same letters to mean different things. Someone buys an A5 cover and an A5 insert from different makers and the insert sticks out by a centimetre. The sizes below are the ones you will actually meet, with the dimensions that matter, so that a cover and its refills come from the same measurement and not just the same name.
If you want the quick pick: A5 for a desk or a daily journal, B6 for a bag that is not a laptop bag, A6 or 3.5 by 5.5 inch pocket for a jacket or back pocket. Buy the cover after you have found the insert you want to write in.
The ISO sizes: A5, A6, B6
The A series is the international paper standard. Each size is half the one before. A4 is a sheet of printer paper in most of the world, 210 by 297 mm. A5 is half of that, 148 by 210 mm, the size of most hardback journals. A6 is half again, 105 by 148 mm, a true pocket size.
The B series sits between the A sizes. B6 is 128 by 182 mm, noticeably smaller than A5 and larger than A6. It has become popular in the last decade because it fits a small bag and still gives a usable page. B5, 176 by 250 mm, is the large lecture-notebook size.
Covers and inserts labelled with these sizes should match across makers. In practice there is a tolerance of a few millimetres, and a hardback notebook described as A5 is often a little larger than the paper inside it, which is why a hardback does not fit an A5 leather cover made for softcover inserts.
The traveler’s size
The tall, narrow leather covers with elastic bands that hold two or three stapled inserts use a size of their own: 110 by 210 mm for the regular, and about 90 by 125 mm for the passport version. The regular is A5 height but 38 mm narrower.
This is the mismatch that catches most people. An A5 insert is too wide for a traveler’s cover; a traveler’s insert leaves a wide gap in an A5 cover. Some makers sell the traveler’s size as “A5 slim”, which is accurate as long as you check the width.
US sizes
Letter is 8.5 by 11 inches, 216 by 279 mm. Half letter, 5.5 by 8.5 inches, is the American near-equivalent of A5 and most A5 covers tolerate it. Pocket notebooks from American makers are usually 3.5 by 5.5 inches, 89 by 140 mm, a little smaller than A6 in both directions. Covers sold for that size hold an A6 insert only with a bulge.
Choosing a size by where it lives
On a desk, A5 is right. The page holds a full day’s entry or a meeting’s notes, and every ruling, paper and cover you could want exists in A5. B5 if you write large or sketch.
In a bag, B6 or A5 softcover. B6 fits a handbag or a small backpack pocket and stays flat. A5 hardback adds weight and corners.
In a pocket, A6 or 3.5 by 5.5. These are for lists, quick notes and the kind of journal written in fragments. Nobody writes an essay in one.
Thickness, page count and paper weight
Two notebooks of the same size can differ in thickness by a factor of two, because paper weight and page count both add up. A 200-page A5 in heavy 90 gsm paper is a thick book; the same count in a 52 gsm thin paper is a slim one. Our guide to paper for fountain pens covers what weight actually does for ink. For a cover with elastic or a strap, check the maximum spine thickness it will hold.
Binding and whether it lies flat
Sewn or thread-bound notebooks open flat and survive years of use. Glued bindings crack and shed pages. Stapled inserts are thin, cheap and lie flat, which is why the traveler’s system uses them. Spiral and disc bindings fold back on themselves and suit people who write on a knee. If you write across the gutter or near the inside margin, lie-flat matters more than any other binding feature.
Covers: when a refillable one pays off
A leather cover costs several notebooks’ worth up front. It pays off when the inserts you prefer are standard and cheap, and when you intend to keep it for years. It does not pay off if you buy it for a proprietary insert size that one maker sells, because you are then tied to that maker’s paper, price and stock.
Check three numbers before buying any cover: the insert height and width it is built for, the maximum thickness, and whether it holds a hardback or a softcover. Then buy the inserts first and the cover second.
Who should not buy which
Anyone who writes on the go should not buy a hardback A5; it is a desk object. Anyone with large handwriting should not buy A6 and expect to journal in it. And anyone buying a leather cover as a gift should find out which insert the recipient already uses, because the cover that fits nothing they own goes in a drawer.
How we choose notebooks
When we recommend journals, inserts and covers in our journals and paper section, each pick lists the exact dimensions in millimetres, the paper weight, the page count and binding, and which standard inserts a cover takes. Our full process is on the how we choose page.
Final verdict
A5 for the desk, B6 for the bag, A6 or 3.5 by 5.5 for the pocket. Measure inserts in millimetres rather than trusting the letter on the label, keep traveler’s and A5 sizes apart, and buy the insert you like before the cover that will hold it.
Questions people ask
Is A5 the same as half letter?
Close but not identical. A5 is 148 by 210 mm; US half letter is 140 by 216 mm. Covers built for one usually take the other with a few millimetres of slack or overhang, but inserts with elastic closures can sit badly.
What size are Field Notes and similar pocket notebooks?
3.5 by 5.5 inches, about 89 by 140 mm, which is slightly narrower and shorter than A6. Pocket covers are often made specifically for that size and will not hold an A6 refill flat.
What does B6 slim or A5 slim mean?
Same height as the standard size, narrower width. A5 slim is usually about 110 by 210 mm, which is the traveler's notebook insert size under another name. Check the exact numbers, because slim is not standardised.
