Correlations for the interface roughness are proposed for conditions without or with disturbance waves for vertical annular flow. The decisive role of interface roughness in the interfacial friction factor is specified through a comparison of ten correlations for the interfacial friction factor with an experimental database. The effect of the disturbance wave on the interface roughness is analyzed to figure out the influence parameters, which are the superficial gas and liquid Reynolds numbers for conditions without disturbance waves and gas core and liquid film Reynolds numbers for conditions with disturbance waves. The proposed correlations improve the prediction precision of the interfacial friction factor, especially in smooth and transitional regimes.