# Where can I find a table for NIST standards on temperature and pressure?

The Wikipedia article Standard conditions for temperature and pressure notes that IUPAC and NIST are two of the most common standards for temperature and pressure in use.

Even if I could have gotten my hands on the IUPAC standards, I wouldn't have wanted to use them as the standard temperature according to IUPAC is 0 °C. For my present work, which is related to fluid dynamics, NIST standards seem to be useful.

However I couldn't find any solid reference where I could get the related data. The reference listed on wikipedia are weak. NIST's own website is very difficult to navigate. Is there a place where I can find NIST published values for standard temperature and pressure? I am not asking for just the values for temperature and pressure, which if I were to trust most sources, are 293.15 K and 101.325 kPa respectively. But how about the value of density of air at that T&P? What about dynamic viscosity?

The problems created by this inaccessibility of data are so rampant that the aforementioned Wikipedia article includes the following quote (2015 March 25 Wed 2243 hrs):

However, many technical publications (books, journals, advertisements for equipment and machinery) simply state "standard conditions" without specifying them, often leading to confusion and errors. Good practice is to always incorporate the reference conditions of temperature and pressure.

The changes in these quantities (and perhaps in other related quantities), for small changes in both temperature and pressure, are a few percentage points at worst. That's assuming a typical lab setting. However, a great amount of noise could have been eliminated had NIST simply published this data (and made it accessible).

• Did you try the NIST website?
– hft
Mar 26, 2015 at 6:17
• Yes I did. I couldn't find it. I also tried googling nist standard atmospheric pressure and temperature but none of the results are directly relevant. They have partial answers of my questions. I need one place where everything is listed. Mar 26, 2015 at 6:20
• webbook.nist.gov/chemistry Mar 26, 2015 at 15:36
• @pentane That's a really good link. I got to webbook.nist.gov/chemistry/fluid from there. I think my question could have been wrong — though it surprises me a bit. Dry air is not listed as one of the species. Perhaps there isn't an agreed upon standard for the composition of dry air. Which is kind of a bummer as a standard for the same is badly needed. And I don't suppose it's all that difficult to arrive at one. Typical constituents are more or less constant and publishing the results for a laundry list of experiments should be easy from thereon. Mar 26, 2015 at 17:15
• I cannot find a clear definition of "normal temperature and pressure" (NTP) at NIST either. The closes I've come is this article. Furthermore, a google search such as this yields confusing documents that imply that NTP corresponds to a temperature of 21 degC instead of 20 degC. Aug 15, 2016 at 20:21

This is a good question. Wikipedia says the NIST standard is $20^\circ {\rm C}$ and $1\,{\rm atm}$, but the WebBook guide does not define standard conditions. The guide does say "Unless stated otherwise, all data are for reactions occurring at $298\,{\rm K}$," which is $25^\circ{\rm C}$.

Modern Thermodynamics with Statistical Mechanics by Carl S. Helrich says the NIST standard in $25^\circ{\rm C}$ and $1\,{\rm bar}$.

One other thing. The NIST Chemistry WebBook references their enthalpy data to $25^\circ{\rm C}$. That is, if you use the Shomate coefficients to calculate the the enthalpy as a function of temperature, the equation gives $H(T) - H(298.15\,{\rm K})$.

• Took the liberty of editing your formatting a little bit, you can click 'edit' to see what I did, if you like. Mar 2, 2017 at 1:20

I found another reference. The documentation for the JANAF tables states that the standard state is 25 C and 1 bar. (http://kinetics.nist.gov/janaf/pdf/JANAF-FourthEd-1998-1Vol1-Intro.pdf)

I'm walking down this same path and found a reference for the 20C as the Normal Temperature (Doiron 2007). I have, thus far, been unable to find a similar reference to Normal Pressure.

Doiron, Theodore D. 2007. “20°C—A Short History of the Standard Reference Temperature for Industrial Dimensional Measurements.” Journal of Research of the National Institute of Standards and Technology 112 (1): 1–23.

https://nvlpubs.nist.gov/nistpubs/jres/83/jresv83n5p419_A1b.pdf

Page 426: "standard conditions are taken to be To = 273.15K, Po = 101325 Pa"

• The full sentence actually is "If standard conditions are taken to be [...]". Feb 4, 2021 at 10:13