Nib Sizes Explained: EF to Broad, and What Actually Changes on Paper

The letters stamped on a fountain pen nib — EF, F, M, B, BB, or a stub size like 1.1 or 1.5 — aren't a vague size category the way "small, medium, large" is on a t-shirt. They're a real, if approximate, line-width specification, and knowing the actual numbers behind the letters makes choosing a nib a lot less like guessing.

The Western round-nib scale, in millimetres

Extra Fine (EF) lays down a line around 0.3mm wide. Fine (F) runs about 0.5mm. Medium (M) — the most common default — is roughly 0.7mm. Broad (B) comes in around 0.9mm, and Double Broad (BB) around 1.1mm. Each step up roughly doubles the amount of ink the nib deposits per unit length of stroke, which is why the jump from Fine to Broad feels much bigger on paper than the millimetre difference alone suggests — you're not just getting a wider line, you're getting a noticeably wetter one.

What actually changes as width increases

Three things shift together as you move from EF toward BB. First, legibility at small sizes: a finer nib keeps small, dense handwriting readable, while a broad nib on the same small script tends to blur individual letters together as the strokes get close to touching. Second, ink shading and sheen — the visible light-to-dark variation and shimmer some inks show — becomes more pronounced on wider nibs simply because there's more ink pooling per stroke for those effects to show up in; a fine nib can mute an ink's shading almost completely. Third, and often overlooked, bleed-through risk: since a wider nib deposits more ink per stroke, the same paper that handles a fine nib's line without issue can start ghosting or bleeding under a broad or double-broad one, which is exactly the interaction our nib & paper compatibility chart is built to estimate for a specific nib-and-paper combination.

Stub and italic nibs: a different shape, not just a width

Stub nibs — commonly available around 1.1mm and 1.5mm — aren't simply "broad" nibs; they're ground with a flatter, wider tip edge than a round nib, which produces genuine line-width variation within a single letter: thick on the down-strokes, thin on the cross-strokes, giving handwriting a calligraphic look without needing calligraphy technique. A 1.1mm stub is a common everyday choice for people who want some of that flair without the boldness or paper demands of a full broad round nib, while a 1.5mm stub is generally reserved for headings, envelopes, and more deliberately expressive writing rather than dense daily notes.

The Japanese-vs-Western offset that trips up first-time buyers

One detail catches a lot of people switching between brands: nibs from Japanese makers — Pilot, Sailor, and Platinum among the best known — run roughly one size finer than their Western-labeled equivalent. A Japanese Medium writes close to a Western Fine; a Japanese Fine writes close to a Western Extra Fine. This isn't a manufacturing inconsistency, it's a genuine, consistent regional difference in how the letter grades are calibrated, and it matters most if you already own a Western-brand pen in a size you like and are buying a Japanese pen expecting the same letter to feel identical — it generally won't. If you like a thinner line and are buying Japanese, sizing up a notch from your usual Western preference (or down a notch if buying Western after getting used to Japanese) is the practical fix.

Choosing a size for what you're actually writing

Dense small handwriting — bullet-journal entries, marginal notes, cramped forms — favors EF or F, both for legibility and to reduce bleed-through risk on ordinary paper. General everyday writing, letters, and journaling are the classic Medium territory, wide enough to show off ink character without being unwieldy. Broad and Double Broad make the most sense for people who write in larger script, sign their name often, or specifically want maximum shading and sheen from an ink built to show it off — and who are writing on paper heavy and well-sized enough to take the extra ink without bleeding through, which is worth checking before committing to a wider nib as a daily writer.

Line width isn't the only variable

Two pens both labeled "Medium" from different makers can still write slightly different actual widths, since the letter grades are a convention each brand calibrates somewhat independently, not a strict international standard enforced across the industry. The millimetre figures above are genuinely useful reference points, but if a specific line width matters a great deal to you — say, for filling in small printed forms — testing the exact pen (or checking a specific written review of that model) beats relying on the letter grade alone.

Wetness is a separate dial from width, and the two combine

Nib width and how "wet" a nib runs — how generously it feeds ink regardless of the tipping's physical size — are related but genuinely separate properties, and it's easy to conflate them. Two nibs of the identical EF width can still lay down noticeably different amounts of ink if one is tuned to run drier and the other wetter, which is why "get a fine nib for less bleed-through" is good general advice but not a guarantee on its own — a very wet-running Fine nib can still challenge marginal paper more than a drier-running Medium would. This is also why the same nib width can feel completely different between two pen brands even at an identical millimetre spec: wetness is a tuning choice in the feed design, layered on top of the width spec the letter grade actually describes.

Flow and feedback: what a nib "feels" like beyond its width

Beyond width and wetness, nibs vary in how much tactile feedback they give — some glide almost frictionlessly, described as "buttery," while others offer a bit more resistance or texture against the paper, sometimes called "toothy" or having "feedback." Neither is objectively better; it's a matter of personal preference, and it's a property that isn't captured by the EF-to-BB letter grade at all, since it comes from exactly how the tipping material was ground and polished rather than from the nib's width. Two Medium nibs, identical in millimetre width, can feel completely different to write with for this reason — which is one more argument for treating the letter-and-millimetre spec as a starting filter rather than the complete picture of how a specific pen will actually feel in hand.

None of this means the millimetre figures in this guide are unreliable — they're a genuinely useful, consistent starting reference across the whole EF-to-BB range — it just means "nib width" is the first filter in choosing a nib, not the only one, and pairing the width spec with a wetness and feedback preference (learned mostly through hands-on experience with a few different pens) rounds out a much more complete picture of what a given nib will actually feel like in daily use.

Custom nib grinding: changing a nib after purchase

Beyond the factory-ground sizes covered above, specialist nib grinders (either independent craftspeople or in-house services offered by some retailers) can reshape an existing nib into a custom grind — a specific stub angle, an unusually fine "needlepoint" tip, an architect grind (a stub-like shape favored for its distinctive squared-off line variation), or a size adjustment within limits — tailored to one writer's hand, grip angle, and preferences in a way no factory size ever quite matches for everyone. This is a meaningfully different service from simply buying a different stock nib size: a skilled custom grind can address a specific complaint (scratchiness at a particular grip angle, wanting more line variation than a stock stub offers) that swapping to another off-the-shelf width might not fully solve.

Custom grinding isn't something to consider for a first pen — it's a refinement for someone who already knows their preferences well enough to describe a specific problem or desired effect to a grinder, and it typically costs a meaningful amount relative to a mid-range pen's price, on top of the pen itself. It's worth knowing this option exists mainly because it explains why some experienced fountain-pen users have nibs that don't match any letter grade discussed in this guide at all — a custom grind is, by definition, outside the standard EF-to-BB and stub taxonomy, built around one specific hand rather than a factory average.