Grieves’ “drying index” is widely accepted to define drying oils:
Drying index=(Percentage of fatty acids with 2 double bonds)+2*(Percentage of fatty acids with 3 double bonds)
Oils having a drying index greater than 70 are classified as drying oils. Grieves’ formula cannot be applied to oils containing conjugate unsaturated fatty acids. “
Iodine value” is also utilized to identify drying tendency.