A Zahn cup is a viscosity measurement device widely used in the paint industry. It is commonly a stainless steel cup with a tiny hole drilled in the center of the bottom of the cup. There is also a long handle attached to the sides. 5 specifications of cups exist, labeled Zahn cup #x, where x is the number from 1 thru 5. Use large number cup sizes when viscosity if high, use low number cup sizes when viscosity is low.

To find the viscosity of a paint, dip and completely fill the cup with the substance. Vertically lift the cup out of the substance and begin timing with a stopwatch as the substance flows out. When the liquid stream breaks, stop the watch; this corresponding time is the "efflux time".

On paint standard specifications, one denotes viscosity in this manner: efflux time, Zahn cup number.

Conversion

One can convert efflux time to kinematic viscosity (cSt) by using an equation for each cup specification number, where t is the efflux time and ν is the kinematic viscosity.

• Zahn Cup #1 : ν = 1.1 * (t - 29)
• Zahn Cup #2 : ν = 3.5 * (t - 14)
• Zahn Cup #3 : ν = 11.7 * (t - 7.5)
• Zahn Cup #4 : ν = 14.8 * (t - 5)
• Zahn Cup #5 : ν = 23 * t

See also

• Viscosity
• Stormer viscometer

References

External links

• Zahn cup operation reference

Measuring instruments