Ink Viscosity Converter
Convert between centipoise (cP), Zahn cup seconds, and Ford cup seconds for ink and coating viscosity measurements.
Type in any field — the others update instantly. Conversions are approximate.
Ink viscosity measures how thick or thin a fluid is. Lower viscosity means thinner and more runny, while higher viscosity means thicker and more resistant to flow.
Common viscosity units for inks and coatings:
- Centipoise (cP): The standard scientific unit for dynamic viscosity. Water is about 1 cP at 20C.
- Zahn Cup #2: A simple dip cup with a calibrated hole in the bottom. You dip it in the fluid, lift it out, and time how many seconds the fluid takes to drain completely. This is the most common cup for printing inks.
- Ford Cup #4: A similar concept but a different standard cup size used more commonly in the paint and coatings industry. Also measured in seconds.
Approximate conversion formulas:
- Zahn #2 to cP: cP = 3.5 x (seconds - 14), valid for approximately 20-80 seconds
- Ford #4 to cP: cP = 3.85 x (seconds - 12.5), valid for approximately 20-100 seconds
- These conversions are approximate because cup viscometers measure kinematic viscosity, and the relationship to dynamic viscosity (cP) depends on the fluid density.
Typical ink viscosities by application:
| Ink Type | Viscosity (cP) | Zahn #2 (seconds) |
|---|---|---|
| Inkjet ink | 3-15 | Too thin to measure |
| Flexographic ink | 20-60 | 18-30 |
| Gravure ink | 15-35 | 18-24 |
| Screen printing ink | 1,000-10,000 | Too thick to measure |
| Offset lithographic ink | 50,000-150,000 | Too thick to measure |
Practical tips:
- Zahn cups work best for thin to medium viscosity inks such as flexographic and gravure.
- Ford cups are better for paints, varnishes, and medium-viscosity coatings.
- Temperature significantly affects viscosity measurements, so always test at a consistent temperature, typically 25C (77F).
- When thinning ink with solvent, add small amounts and re-measure after each addition to avoid over-thinning.