A pain scale measures a patient's pain intensity or other features. Pain scales are a common communication tool in medical contexts, and are used in a variety of medical settings. Pain scales are a necessity to assist with better assessment of pain and patient screening. Pain measurements help determine the severity, type, and duration of the pain, and are used to make an accurate diagnosis, determine a treatment plan, and evaluate the effectiveness of treatment. Accurately measuring pain is a necessity in medical settings, especially if the pain measurement is going to be used as a screening tool, either for potential diseases or medical problems, or as a type of triage to determine urgency of one patient over another. Pain scales are based on trust, cartoons (behavioral), or imaginary data, and are available for neonates, infants, children, adolescents, adults, seniors, and persons whose communication is impaired. Pain assessments are often regarded as "the 5th Vital Sign".

It is important to understand what features of pain scales are most useful, least useful, and which aid in understanding. In fact, a patient's self-reported pain is so critical in the pain assessment method that it has been described as the "most valid measure" of pain. The focus on patient report of pain is an essential aspect of any pain scale, but there are additional features that should be included in a pain scale. In addition to focusing on the patient's perspective, a pain scale should also be free of bias, accurate and reliable, able to differentiate between pain and other undesired emotions, absolute not relative, and able to act as a predictor or screening tool.