Fountain Pen Nib Sizes Explained

The nib is the heart of a fountain pen — the shaped metal point that meets the paper and decides how wide, wet, and characterful your line turns out. Nib sizes look simple on a chart, but a few quirks trip up almost everyone new to the hobby, especially the gap between how Western and Japanese makers label the same widths. Here’s what the letters mean and how to predict the line you’ll actually get.

The standard width letters

Most round nibs are sold by a single letter that describes how much line they lay down. From finest to broadest, the common Western sizes run roughly:

• EF (extra fine): around 0.4 mm — a thin, precise line for small handwriting and tight margins.
• F (fine): around 0.5 to 0.6 mm — still crisp, a touch more forgiving than EF.
• M (medium): around 0.7 mm — the balanced all-rounder most pens ship with.
• B (broad): around 0.9 to 1.0 mm — a bold, wet line that shows off ink color and shading.

These are approximate. A nib’s stated size is a starting point, not a precise measurement, because the real line width depends on more than the tipping alone.

The Japanese-versus-Western catch

Here is the single most important thing to know before buying online: Japanese nibs run about one full size finer than their Western equivalents. The major Japanese makers — Pilot, Sailor, and Platinum — grind their points narrower than European houses such as Pelikan, Lamy, and Montblanc. As a rule of thumb:

A Japanese Medium writes roughly like a Western Fine.

So if you love a fine line, a Japanese Fine will be very thin indeed, while a European Medium will feel generous and wet. Ignore this and a pen ordered sight-unseen can land a size or more away from what you pictured. When you’re comparing a Japanese nib against a European one, our nib size converter lines the two systems up so you know what you’re really ordering.

Shaped nibs: stub, italic, and oblique

Not every nib is a plain round point. Shaped nibs deliberately vary the line to add character:

• Stub: a broad, rounded edge that writes thick on downstrokes and thinner on cross-strokes, giving handwriting a gentle calligraphic flair while staying easy to use.
• Italic: like a stub but with sharper, crisper corners — more dramatic line variation, but less forgiving of a careless angle.
• Oblique: a point cut at an angle to suit writers who rotate the pen in the hand, keeping the sweet spot aligned with the paper.

Why the same nib can write differently

Two people can put identical nibs to paper and get noticeably different lines, because tipping size is only part of the equation. Three other factors matter:

• Ink wetness: a free-flowing, wet ink spreads wider than a dry one, effectively bumping your line up a size.
• Paper absorbency: cheap, uncoated paper drinks ink and lets it spread along the fibers, widening the line; coated paper keeps it tight.
• Writing angle and speed: more pressure and a slower hand both let more ink down onto the page.

This is why the same Western Medium can look like a fine line on smooth paper with a dry ink, and a broad one on absorbent paper with a wet ink.

A few conversions worked out

The rule of thumb — a Japanese nib runs about one size finer — holds up when you actually run the numbers through a converter rather than eyeballing a chart. A Japanese Medium, at a typical 0.5 mm, matches a Western Fine, also close to 0.5 mm; a Western Fine converts the other direction to a Japanese Medium for the same reason. Go one size finer and a Western Extra Fine, at roughly 0.4 mm, is closest to a Japanese Fine at about 0.35 mm — not an exact match, but the nearest available size. And at the broader end, a Japanese Broad, at roughly 0.7 mm, lines up with a Western Medium rather than a Western Broad. That last one catches people out: ordering a Japanese Broad expecting something like a Western Broad’s bold 0.9–1.0 mm line will land a size and a half short of what you pictured.

What the difference looks like on the page

A 0.2 mm gap between a Western Medium and a Japanese Fine sounds trivial until you see it written out. On a page of cursive handwriting, that’s roughly the difference between a line that reads as ordinary body text and one that reads as noticeably fine print — enough that side-by-side samples from the two pens are usually easy to tell apart at a glance, even without knowing nib sizes. It matters most in two places: cross-hatching and fine shading, where a narrower Japanese nib packs more lines into the same space before they merge into a solid tone, and dense handwriting in a small notebook, where every fraction of a millimeter changes how many words fit on a line before crowding sets in. It matters least on a single bold signature or a page of loose notes, where a size difference this small barely registers.

Steel versus gold: does the metal change the size?

Nib material is a separate axis from size, and it’s easy to conflate the two. Steel nibs are stiffer and more consistent, hold their tipping shape well, and are what most nibs at typical price points are made from; gold nibs (usually 14k or 18k) are alloyed to be springier, giving a small amount of natural flex and softness under pressure that steel doesn’t have, which is why the same nominal size can feel subtly different in gold versus steel even when the stated width is identical. Neither metal makes a nib objectively wider — the tipping material, a hard alloy welded to the nib’s point, is what actually touches the paper and defines the line, and that’s consistent across steel and gold nibs from the same maker. What the metal changes is feel: how much the nib gives under pressure, not the number on a chart.

Why the two traditions diverged

There isn’t a single standards body that pins down what “Fine” or “Medium” must measure — each maker grinds nibs to its own convention, and Japanese and Western makers settled on different defaults as their industries developed largely independently over the decades. The practical result is that the letters on a nib are a within-brand promise, not a cross-brand one: a Pilot Fine and a Sailor Fine sit close to each other, and a Lamy Medium and a Pelikan Medium sit close to each other, but the gap between the Japanese cluster and the Western cluster is consistent enough to plan around — which is exactly why the one-size-finer rule of thumb works as well as it does.

When precision matters more than the label

For most everyday writing, a size that lands close to what you expected is good enough. For technical pens, calligraphy nibs bought to match an existing set, or any purchase with no return policy, treat the printed size as a starting estimate rather than a guarantee, and where possible check a maker’s own published width in millimeters rather than relying on the letter alone — some makers publish exact figures, and those are always more reliable than a general Western/Japanese rule of thumb.

Checking before you buy

Because the labels alone can mislead, it’s worth converting before ordering anything sight-unseen, especially across the Japanese/Western line. Our nib size converter handles a single conversion in a couple of clicks, and the fuller nib size & dry time reference lays out every size in both standards side by side, along with how each size dries on four common paper types — useful if you’re choosing a nib and a paper stock at the same time. For a deeper look at exactly what a Japanese/Western mismatch changes about how a line looks and behaves on the page, see a Japanese Medium nib isn’t a Western Medium.

Which size should you pick?

If you write small or your handwriting is compact, lean fine — EF or F in a Western pen, and remember that a Japanese F will be finer still. If you want to enjoy ink shading and sheen, or your hand is larger, a Medium or Broad gives the ink room to show off. For a first fountain pen, a Western Fine or Medium is the safe, versatile choice: wet enough to feel smooth without flooding ordinary paper. From there you can branch into stubs and broads once you know what kind of line makes you want to keep writing.

Flex nibs, briefly

A small category of nibs, mostly vintage and a handful of modern reproductions, are ground to flex under pressure — pressing down spreads the tines and widens the line dramatically within a single stroke, the way copperplate calligraphy achieves its thick downstrokes and thin upstrokes with one nib rather than a dedicated stub. Flex nibs aren’t described by the EF-to-BB scale at all, since their whole point is that the width changes within a single letter; they’re a specialist tool for a specific style of writing rather than a general-purpose size choice.