Colorimetry is a method for determining the concentration of coloured substances in a solution. The intensity of colour is directly proportional to the concentration of compound being measured. Smartphone based colorimetry has grown in popularity as analytical instruments due to their low cost and ability to collect, store and process data all in one device. In smartphone colorimetry, the camera on the phone serves as a detector. The colorimetric method based on a smartphone and the UV method both are based on the detection of colour intensity. The ammonium metavanadate is having different oxidation states and it produce different colours in its oxidation state. The +5-oxidation state shows yellow colour, +4 oxidation state shows blue colour, +3 oxidation state shows green colour and +2 oxidation state shows purple colour. The ammonium metavanadate reagent is orange red in colour; however, it transforms into green colour complex when it reacts with drugs containing nitrogen, phosphorus and sulphur in its structure. In this article the developed method for all the drugs exhibits good linearity having Correlation coefficient about 0.998(Amoxicillin trihydrate), 0.998 (Silodosin) and for 0.999(Sofosbuvir). With increasing the concentrations of API, the colour intensity increases. All photographs were taken with smartphone and analysed using the photometrix PRO software. This application converts an image to an RGB histogram and regression models are included into the photometrix PRO application. By using Photometrix PRO and UV technique, the percent RSD of for all the three drugs was  Using statistical tool i.e two paired test on both procedures for all the three different drugs, the results show that both are equally significant. Keywords: UV spectrophotometry, Smartphone based colorimetry, Photometrix PRO, RGB Histogram