The intensity of sound is measured in watt per square metre (Wm-2). The faintest sound that a human ear can detect at a frequency of 1000 Hz corresponds to an intensity of about 10-12 Wm-2. It is called the threshold of hearing. Similarly, the loudest sound that the human ear can tolerate corresponds to an intensity of about 1 Wm-2. It is called the threshold of pain.