A UV dosimetry system comprises a wearable unit and a mobile computing device. The wearable unit measures the UV irradiance intensity and wirelessly communicates with the mobile computing device. The UV dosimetry system supports multi-user control and can link one mobile computing device with multiple wearable units. The UV dosimetry system processes the measured UV irradiance intensity to calculate the UV index (UVI) and the sensor site specific UV dose. It can also calculate the total absorbed UV dose and vitamin D production by taking into account user specific factors. The UVI data measured by a plurality of UV meters such as the disclosed UV dosimetry system are crowd sourced to a remote server together with the location and time data of the measurement. The remote server excludes invalid UVI measurement and generates UVI maps showing time-varying distribution of UVI data at different locations.