Ford Cup Viscosity Converter

Convert Ford Cup efflux time to kinematic viscosity (cSt) and dynamic viscosity (cP). Select your cup, enter the drain time and coating density.

Select Ford Cup

⌀ 2.53 mm

21 – 100 s

Thin fluids

⌀ 4.00 mm

20 – 100 s

Most common

⌀ 3.40 mm

20 – 100 s

Mid-range

⌀ 5.20 mm

23 – 100 s

Thick fluids

Active Equation — Ford Cup #4

cSt = (0.233 × t) − (179 ÷ t) | ISO 2431

Efflux Time (seconds) Valid range: 20 – 100 s for #4

Coating Density (g/cm³) optional Needed for dynamic viscosity (cP)

Enter efflux time to check measurement validity

Kinematic Viscosity

—

Dynamic Viscosity

Enter density

Practical Note

Ford Cup #4 is the most widely used cup in coatings and adhesives formulation. It covers the viscosity range typical of most solvent-based and waterborne systems. If your fluid drains faster than 20 seconds, switch to Cup #2. If it drains slower than 100 seconds, switch to Cup #5.

Conversion based on ISO 2431 standard. Kinematic viscosity (cSt) = Dynamic viscosity (cP) ÷ Density (g/cm³). Results are valid only within the stated efflux time range for each cup — outside this range, turbulence or surface tension effects make the correlation unreliable.

Built by PolymerDNA — more formulation references in the Formulae Masterbook.