Colloquially, room temperature is the range of air temperatures that most people prefer for indoor settings, which feel comfortable when wearing typical indoor clothing. Human comfort can extend beyond this range depending on humidity, air circulation and other factors. In certain fields, like science and engineering, and within a particular context, room temperature can mean different agreed-on ranges. In contrast, ambient temperature is the actual temperature of the air (or other medium and surroundings) in any particular place, as measured by a thermometer. It may be very different from usual room temperature, for example an unheated room in winter.
The American Heritage Dictionary of the English Language identifies room temperature as around 20–22 °C (68–72 °F), while the Oxford English Dictionary states 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 23–25.5 °C (73–78 °F), with that for winter being 20–23.5 °C (68–74 °F), although by other considerations the maximum should be below 24 °C (75 °F) – and to avoid sick building syndrome, below 22 °C (72 °F).
The World Health Organization in 1987 found that comfortable indoor temperatures between 18–24 °C (64–75 °F) were not associated with health risks for healthy adults with appropriate clothing, humidity, and other factors. For infants, the very elderly, and those with significant health problems, a minimum 20 °C (68 °F) was recommended. Temperatures lower than 16 °C (61 °F) with humidity above 65% were associated with respiratory hazards including allergies.
The WHO's 2018 guidelines give a strong recommendation that a minimum of 18 °C (64 °F) is a "safe and well-balanced indoor temperature to protect the health of general populations during cold seasons", while a higher minimum may be necessary for vulnerable groups including children, the elderly, and people with cardiorespiratory disease and other chronic illnesses. The recommendation regarding risk of exposure to high indoor temperatures is only "conditional". Minimal-risk high temperatures range from about 21–30 °C (70–86 °F) depending on the region, with maximum acceptable temperatures between 25–32 °C (77–90 °F).
Temperature ranges are 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 15 to 25 °C (59 to 77 °F), with room temperature being 1 to 30 °C (34 to 86 °F). Merriam-Webster gives as a medical definition a range of 15 to 25 °C (59 to 77 °F) as being suitable for human occupancy, and at which laboratory experiments are usually performed.
People traditionally serve red wine at room temperature. This practice dates 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). It is therefore advised to serve red wine at a temperature of at most 18 °C (64 °F).
126.96.36.199 Definition of Room Temperature: According to the United States Pharmacopeia National Forumlary [sic] (USP-NF), the definition 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.