While sound is most commonly measured in decibels, it can also be measured in hertz for other purposes. Decibels measure the volume of sound, while hertz are used to measure the frequency.
Sounds occur when something vibrates and causes pressure waves. Human ears sense these pressure waves and interpret them as sounds. The sounds vary in intensity depending on how much energy is within the wave. More energy equates to more intense sounds. This intensity is measured in decibels with the aid of a decibel meter. Once the intensity is determined, the frequency (the number of vibrations made by the wave per second) can be measured in hertz.