# What is considered room temperature in Celsius?

Recently, I have seen room temperature listed at 20 °C and 25 °C. Which one is more accurate for use in chemistry problems?

• Before the 1970s energy crisis, it was 25, afterwards 20. There is no way of knowing unless it is specified explicitly. – Karsten Theis Dec 12 '19 at 14:55
• In high school and college, we used standard temperature & pressure, 59F, 29.92 inches of Mercury (sea level) for calculations. – CrossRoads Dec 12 '19 at 15:16
• Room temperature in my labs in Germany was somewhere just above $\pu{20^\circ C}$. Room temperature at my previous lab in Japan was $\pu{25^\circ C}$ in summer and $\pu{20 ^\circ C}$ in winter. Room temperature at my current lab in Japan was around $\pu{30^\circ C}$ in summer and is now around $\pu{15 ^\circ C}$. Yes, I died in summer. – Jan Dec 12 '19 at 16:50

Considering you've read Wikipedia article on room temperature (r.t.), you probably already have an idea that there is no uniformly defined value due to the subjective matter the term is defined upon. There are numerous standards across industries defining temperature ranges, most of which lead to the value for r.t. of $$\pu{(20 ± 5) °C}.$$

In natural sciences there are several well-defined standard conditions describing the combination of exact values for temperature, pressure and humidity. Room temperature is not among these, so ideally, an exact value must be specified alongside, if relevant, e.g. "the parameter has been determined at r.t. $$(\pu{20 °C})$$".

German Wikipedia article presents an observation that in physical chemistry and statistical physics in European region the typical value taken for r.t. is $$\pu{20 °C},$$ whereas in U.S.A. the majority of textbooks refer to r.t. as to $$\pu{25 °C}.$$

In nuclear chemistry, thermal neutron energy $$E_0 = \pu{25.26 meV}$$ is fixed as characteristic energy at r.t., which is a reference point for tabulated parameters such as neutron cross section. Using $$E = k_\mathrm{B}T$$ relation, an exact value for r.t. can be determined, which is usually taken as $$\pu{20.43 °C}$$ (see e.g. [1, p. 11-173] and references therein).

### References

1. Haynes, W. M.; Lide, D. R.; Bruno, T. J. CRC Handbook of Chemistry and Physics: A Ready-Reference Book of Chemical and Physical Data, 97th ed.; Taylor & Francis Group (CRC Press): Boca Raton, FL, 2016. ISBN 978-1-4987-5429-3.
• I agree with your argument. But why only USA use the value $\pu{25 ^\circ C}$? For example, we always teach the room temperature as $\pu{298 K}$, which has coveted to $\pu{25 ^\circ C}$. – Mathew Mahindaratne Dec 12 '19 at 18:34
• @MathewMahindaratne I didn't attribute any geographical exclusivity to one value or another, only a note on a trend which I fairly loosely translated from German article. And since your profile says you are from Texas, USA and you teach 25 °C, whereas I'm from Russia (European part, so I think it counts:) ) and I usually would attribute r.t. to 20 °C, this trend seem to be accurate. – andselisk Dec 12 '19 at 18:48
• I think it should be a fixed value internationally, regardless of what part you are form, for better understanding. Thasnks for the explanation. – Mathew Mahindaratne Dec 12 '19 at 20:58
• The (broadly international) community for thermodynamics of phases and alloys, heavily favors 298K as the reference temperature. – Jon Custer Dec 13 '19 at 3:14