There are a lot of units used in Anesthesiology field. Sometimes, we could not compare two units describing the same physical category. For example, I cannot find reference materials explaining whether a 7 French catheter is larger than a 16 Gauge catheter. Furthermore, I would like to know why there are so many differences of blood calcium levels between regular check and intraoperative emergency reports. As for liquid drug concentrations, we usually use the mg/ml during a clinical practice, however, basic researchers report it as mole/liter (molarity, M). I would like to answer these questions. So, I have searched some references and have summarized them to explain length, concentration, temperature, particle size, pressure, and ratio units commonly used in our clinical practice, Anesthesiology.