There is provided an apparatus (100) for determining a blood pressure measurement for a subject (102). The apparatus (100) comprises a processor (104) configured to acquire, from a light sensor (106), measurements of an intensity of light (108) of a first wavelength range reflected from the skin (110) of the subject (102) and an intensity of light (112) of a second wavelength range reflected from the skin (110) of the subject (102) for a range of forces at which the light sensor (106) is applied to the skin (110). The processor (104) is also configured to determine a ratio of the intensity of light (108) of the first wavelength range to the intensity of light (112) of the second wavelength range for each of the applied forces and determine a blood pressure measurement for the subject (102) based on an integral of the ratios with respect to the applied forces.
