Devices and methods for determining the thickness of hair are provided. An exemplary device includes a computing unit with a processor and a local memory. The processor is connected to the local memory and configured to read data from and/or to write data into the local memory. The device further includes a user input/output unit configured for interaction with a user. Also, the computing unit includes an image data input interface for receiving image data of at least one individual hair. The image data input interface is connected to the processor. Further, the computing unit includes a user interface connected to the user input/output unit and to the processor. The computing unit is configured to process the image data of the at least one individual hair to create hair thickness values of the at least one individual hair and to output the hair thickness values to the user interface.