Fountain Pen Nib Size Guide | Pick the Right Width

Choosing the right fountain pen nib size comes down to matching line width to your handwriting and paper, with Japanese nibs writing noticeably finer than Western ones.

Picking the wrong first nib is the fastest way to hate a fountain pen. Line width varies so much between brands and continents that a “Medium” from Germany writes thick and wet while a Japanese “Medium” scratches like a fine. Here is the actual breakdown of nib codes, real millimeter measurements, and the regional gap that catches most US buyers.

Standard Nib Sizes and How They Write

Nib sizes refer to the line the nib produces, not the metal tip’s physical width. The code system is universal, but the actual output spans nearly a full millimeter depending on the maker. The table below shows the Western consensus ranges.

A “Medium” is the default on most new pens and usually produces a 0.6 mm line in Western brands. If you are entirely unsure, start there.

Japanese vs. Western Nibs: The Gap You Must Know

Japanese nibs from Pilot, Sailor, or Platinum are ground to write about one full size finer than Western nibs from Lamy, Pelikan, or Faber-Castell. A Japanese Medium writes like a Western Fine, and a Japanese Fine writes like a Western Extra Fine. On standard US notebook paper, that means a Japanese Medium can feel thin and scratchy to someone used to a Western Medium. If you order a Japanese pen, jump up one size — choose Medium or Broad for a line closer to what a Western Medium puts down.

Matching a Nib to Your Handwriting

The wrong nib makes even a great pen feel wrong. Use your existing ballpoint or gel pen as a ruler. Measure the line it makes, then find the matching fountain nib above. For handwriting size itself: small and compact script wants an EF or F; average writing fits a Medium; large or flourished lettering needs Broad, Double Broad, or a Stub. When testing a pen, write full sentences at normal speed, not circles or figure-eights — only real writing reveals smoothness, feedback, wetness, and starting reliability. A pen that passes all five checks is the right one.

Once you know your ideal size, the next step is finding a pen that fits your budget. Our roundup of the best budget fountain pens under $50 covers models that pair well with Fine, Medium, and Broad nibs without breaking the bank.

Physical Nib Numbers (#5 vs. #6) and Compatibility

Separate from line width, nibs also have a number like #5 or #6. That number refers to the inner diameter of the nib in millimeters, which determines what feed and pen body it fits. A #6 nib is the most common size and the standard for many mid-range pens. #5 nibs are smaller and found on slimmer models; #7 and #8 are larger and typically appear on high-end or oversized pens. When ordering a replacement nib, match the number to your pen’s feed diameter — a #6 nib fits a 6 mm feed.

Common Mistakes and What to Avoid

Assuming One “Medium” Fits All

A Medium from Lamy and a Medium from Pilot are not the same. Width varies by brand and by continent. Do not assume a pen will write like your last one just because the code matches.

Paper Makes the Nib

Fine and Extra Fine nibs work well on standard or absorbent paper because they deposit less ink and resist feathering. Broad and Double Broad nibs dump noticeably more ink and can bleed through cheap notebook paper. If you write broad, buy quality paper. If you write fine, you have more freedom.

Ink Showcasing Needs a Broad Nib

Shading, sheen, and shimmer are invisible through an EF line. If you bought ink for its color complexity, pair it with at least a Medium nib — Broad or Stub is better.