Colloquially, room temperature is the range of air temperatures that people prefer for indoor settings, which feel comfortable when wearing typical indoor clothing. As a medical definition, the range generally considered to be suitable for human occupancy is between 15 degrees Celsius (59 degrees Fahrenheit) and 25 °C (77 °F), though human comfort can extend somewhat beyond this range depending on factors such as humidity and air circulation. In certain fields, like science and engineering, and within a particular context, "room temperature" can have varying agreed upon values for temperature.
The American Heritage Dictionary of the English Language identifies room temperature as around 20 to 22 °C (68 to 72 °F), and the Oxford English Dictionary claims that it is "conventionally taken as about 20 °C (68 °F)".
Owing to variations in humidity and likely clothing, recommendations for summer and winter may vary; a suggested typical range for summer is 23 to 25.5 °C (73 to 78 °F), with that for winter being 20 to 23.5 °C (68 to 74 °F), although by other considerations the maximum should be below 24 °C (75 °F) – and for sick building syndrome avoidance, below 22 °C (72 °F).
The World Health Organisation's standard for comfortable warmth is 18 °C (64 °F) for normal, healthy adults who are appropriately dressed. For those with respiratory problems or allergies, they recommend no less than 16 °C (61 °F), and for the sick, disabled, very old or very young, a minimum of 20 °C (68 °F).
Temperature ranges may be defined as room temperature for certain products and processes in industry, science, and consumer goods. For instance, for the shipping and storage of pharmaceuticals, the United States Pharmacopeia-National Formulary (USP-NF) defines controlled room temperature as between 20 to 25 °C (68 to 77 °F), with excursions between 15 to 30 °C (59 to 86 °F) allowed, provided the mean kinetic temperature does not exceed 25 °C (77 °F). The European Pharmacopoeia defines it as being simply 15 to 25 °C (59 to 77 °F), and the Japanese Pharmacopeia defines "ordinary temperature" as being 15 to 25 °C (59 to 77 °F), with "room temperature" being 1 to 30 °C (34 to 86 °F).
Ambient temperature simply means "the temperature of the surrounding air". In any particular room, it is the actual temperature of the air in that room, as measured by a thermometer. It may be very different from usual "room temperature", for example an unheated room in winter.
A common piece of advice is to serve red wine "at room temperature". This advice stems from a time from before central heating, when room temperature in wine-drinking countries was considerably lower than it is today, usually in the range between 15 °C (59 °F) and 18 °C (64 °F). The advice is therefore to serve the wine at, at most, about 18 °C (64 °F).
18.104.22.168 Definition of Room Temperature: According to the United States Pharmacopeia National Forumlary (USP-NF), the definiton of Room Temperature is between 15 and 30 °C in the United States. However, in the EU, the room temperature is defined as being 15 to 25 °C, while in Japan, it is defined being 1 to 30 °C.