Relative viscosity and absolute viscosity are two concepts that describe the viscosity of a fluid, and there are some differences between them.

Relative viscosity:

Relative viscosity refers to the viscosity of a fluid at a certain temperature compared to some reference fluid, usually a solvent. It is determined by measuring the flow properties of the fluid with respect to the reference fluid. Relative viscosity is a dimensionless value that indicates the degree to which the viscosity of the fluid increases with respect to the reference fluid. Relative viscosity can be calculated by measuring the movement time or flow velocity of the fluid.

Relative viscosity is different from absolute viscosity

Absolute viscosity:

Absolute viscosity refers to the actual viscosity of a fluid, also known as dynamic viscosity or dynamic viscosity. It is determined by measuring the volume (flow rate) through which the fluid passes per unit time per unit area. Absolute viscosity is a physical quantity with units, usually used in PASCAL seconds (Pa·s) or millipa ·s (mPa·s).

The absolute viscosity is an intrinsic property of fluid and can be directly used in the calculation and analysis of fluid mechanics. The relative viscosity is the relative value of the reference fluid, which is often used for the measurement of liquid mixtures and the comparison of liquid properties.

North-south tides remind you that the relationship between relative and absolute viscosity can be expressed by a constant, called the constant of proportionality or the conversion factor of relative viscosity to absolute viscosity. This conversion factor depends on the reference fluid and temperature conditions used. To summarize, the relative viscosity is the fluid viscosity comparison value with respect to the reference fluid, while the absolute viscosity is the actual viscous physical quantity of the fluid.