Capacity factor (k') is a signal of how extended an analyte can be retained over the stationary phase. Or analyte has how much interact with the stationary phase. Capacity factor (k') depends as mobile phase, stationary phase, quality of column and temperature.
For better chromatographic performance in isocratic separation capacity factor (k') must be in between 1-10 k'Capacity factor calculated as, k'= (Tr - To) / To.