At one time the petroleum industry relied on measuring kinematic viscosity by means of the Saybolt viscometer, and expressing kinematic viscosity in units of Saybolt Universal Seconds (SUS) and Saybolt Furol Seconds (SFS). This practice is now obsolete in the petroleum industry.

This practice establishes the official equations relating SUS and SFS to the SI kinematic viscosity units, mm²/s.

This practice allows for the conversion between SUS and SFS units and SI units of kinematic viscosity.

1.1 This practice covers the conversion tables and equations for converting kinematic viscosity in mm²/s at any temperature to Saybolt Universal viscosity in Saybolt Universal seconds (SUS) at the same temperature and for converting kinematic viscosity in mm²/s at 122 and 210°F (50 and 98.9°C) to Saybolt Furol viscosity in Saybolt Furol seconds (SFS) at the same temperatures. Kinematic viscosity values are based on water being 1.0034 mm²/s (cSt) at 68°F (20°C).

Note 1—A fundamental and preferred method for measuring kinematic viscosity is by use of kinematic viscometers as outlined in Test Method D 445. It is recommended that kinematic viscosity be reported in millimetres squared per second, instead of Saybolt Universal Seconds (SUS) or Saybolt Furol Seconds (SFS). This method is being retained for the purpose of calculation of kinematic viscosities from SUS and SFS data that appear in past literature. One millimetre squared per second (mm²/s) equals one centistoke (cSt), which is another unit commonly found in older literature.

1.2 The SI unit of kinematic viscosity, mm²/s, and temperature in degrees Fahrenheit are the standard in this practice.