🖋️ Stationery
Fountain Pen Ink & Nib Gauge
Convert ink volume between millilitres, fluid ounces, drops and typical fills, or compare extra-fine to broad nib widths. Choose a category, then press Convert.
About the Fountain Pen Ink & Nib Gauge
Ink volume is straightforward: 1 mL is 1 cm³, a US fluid ounce is 29.574 mL and an imperial fluid ounce is 28.413 mL. A standard international cartridge holds about 0.7 mL, and a converter fill is similar. A drop is usually taken as 0.05 mL, though surface tension and the feed change it.
Nib widths are not standardised. A Japanese fine may write a 0.3 mm line while a European fine writes 0.45 mm, and the same nib lays down more ink on absorbent paper. The millimetre figures here are typical line widths, not a specification you can rely on across brands.
How the calculation works
- 1 mL = 1 cm³; 1 US fl oz = 29.5735 mL; 1 UK fl oz = 28.4131 mL.
- 1 drop ≈ 0.05 mL; 20 drops ≈ 1 mL.
- 1 international cartridge ≈ 0.7 mL; 1 converter fill ≈ 0.7 mL.
- Typical nib line widths: EF 0.3 mm, F 0.4 mm, M 0.5 mm, B 0.6 mm, BB 0.8 mm.
Reference values
| Nib | Typical line width | Character |
|---|---|---|
| Extra fine (EF) | 0.3 mm | Small handwriting, detailed notes |
| Fine (F) | 0.4 mm | Everyday writing |
| Medium (M) | 0.5 mm | Smooth, broad everyday line |
| Broad (B) | 0.6 mm | Signatures, shading inks |
| Double broad (BB) | 0.8 mm | Bold strokes, wet inks |
| Stub 1.1 | 1.1 mm | Line variation |
| Stub 1.5 | 1.5 mm | Calligraphy and headings |
Worked example: how far a bottle goes
A 30 mL bottle at 0.05 mL per drop is about 600 drops; a 0.7 mL cartridge is about 14 drops. At a typical 0.5 mL per page, the bottle fills about 60 pages. Nib widths are nominal: a Japanese fine (0.3–0.4 mm) writes finer than a European medium (0.5–0.6 mm).
Paper changes the line as much as the nib. An absorbent paper spreads the ink and produces a wider, softer line; a coated paper keeps the line crisp and uses less ink. If you are comparing nibs, use the same paper and ink for every sample.