Nib Size Converter
Turn a nib name into a line width in millimetres, and convert between Western and Japanese sizing so you know what you’re really ordering.
Conversion
Line widths are typical values on ordinary paper; a wetter ink or more absorbent paper writes broader.
Typical line widths (mm)
| Size | Western | Japanese |
|---|---|---|
| Extra Fine (EF) | 0.4 | 0.28 |
| Fine (F) | 0.5 | 0.35 |
| Medium (M) | 0.7 | 0.5 |
| Broad (B) | 0.9 | 0.7 |
| Double Broad (BB) | 1.1 | 0.9 |
How the conversion works
The tool looks up the typical line width of your chosen size in the source standard, then finds the size in the target standard whose typical width is closest. That’s why a Japanese Medium maps to a Western Fine — both write around half a millimetre.
Widths are approximate and assume ordinary paper with a mainstream ink. Stubs, italics, and architect grinds shape the line differently and aren’t captured by a single width, so treat those as their own category.
Frequently Asked Questions
Are Japanese nibs really finer than Western ones?
Yes. As a rule of thumb, Japanese nibs (Pilot, Sailor, Platinum) run about one size finer than Western/European nibs (Pelikan, Lamy, Montblanc). A Japanese Medium writes about as wide as a Western Fine, and a Japanese Fine is close to a Western Extra Fine. If you love a crisp thin line, Japanese sizing gets you there.
How wide is each nib size?
Line widths aren't standardised, but typical Western values are roughly EF 0.4 mm, F 0.5 mm, M 0.7 mm, B 0.9 mm, and BB 1.1 mm. Japanese equivalents run finer — around EF 0.28 mm, F 0.35 mm, M 0.5 mm, B 0.7 mm. This tool uses those typical figures.
Why does my nib write wider than the chart says?
The same nib lays down a wider line with a wetter ink, on more absorbent paper, or at a lower writing angle, and a narrower line with a dry ink on coated paper. The chart is a starting point; your ink and paper move the real width around it.
Guide only. Nib widths vary between makers and with ink and paper; check a maker’s own chart or a writing sample when precision matters.