Patients' ratings of pain intensity are an important component of a comprehensive assessment of pain. Although a 10-cm visual analog scale (VAS) is recommended for quantifying subjective pain intensity, a 0 to 5 point numerical rating scale (NRS) is commonly used. These two scales are often viewed as interchangeable or mathematically equivalent, with a 2 on a 0 to 5 point scale seen as equal to a 4 on a 10-cm VAS. The purposes of this study were to compare patients' pain ratings on each scale and to examine nurses' responses to mathematically equivalent pain ratings. Results indicated that patients do not rate their pain in a mathematically equivalent way. VAS ratings were lower than NRS ratings, and more than three quarters of patients provided ratings that were not mathematically equivalent. In addition, nurses provided with fictitious patient scenarios did not provide the same pain medication for equivalent ratings and chose smaller analgesic doses in comparison with experts.