# What is the mass of water? (be precise) **URL:** \ **Category:** Factual Questions\ **Created:** [May 27, 2024, 11:53pm UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162 "2024-05-27T23:53:17Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![Peter\_Morris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peter_morris/32/359_2.png) [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)\ **Post date:** [May 27, 2024, 11:53pm UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/1 "2024-05-27T23:53:17Z")
When the metric system was first invented, mass and volume were tied to water, so that 1 kg was defined as the mass of 1 litre of water at STP , and a litre is a 10x10x10 cube. So 1cc of water had a mass of exactly 1 gram by definition. This is no longer the definition used. Mass and length/distance are base units with their own definitions. So I would expect that 1cc of water is still pretty close to a gram, but not precisely equal. Maybe a tiny bit more or a tiny bit less. So what is the precise mass of exactly 1000 cc of water by current definitions? (Googling doesn’t help. It produces 100s of pages telling me that 1 cc has a mass of 1g. I’m sure the answer is somewhere out there, but after spending half an hour searching fruitlessly, I came here.) ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [May 28, 2024, 12:17am UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/2 "2024-05-28T00:17:06Z")
You need to specify pressure and temperature, but for IUPAC standard temperature and pressure (STP) of 25 °C and 1 bar I get 997.05 kg/m3 from the [US National Institute of Science and Technology (NIST) Chemistry WebBook](https://webbook.nist.gov/cgi/fluid.cgi?ID=C7732185&TUnit=C&PUnit=bar&DUnit=kg%2Fm3&HUnit=kJ%2Fmol&WUnit=m%2Fs&VisUnit=uPa*s&STUnit=N%2Fm&Type=IsoTherm&RefState=DEF&Action=Page). Stranger ---
**Author:** ![N9IWP](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/n9iwp/32/3154_2.png) [@N9IWP](https://boards.straightdope.com/u/N9IWP)\ **Post date:** [May 28, 2024, 12:22am UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/3 "2024-05-28T00:22:33Z")
Depends on the concentration of deuterium, that can add a few femtograms… Brian ---
**Author:** ![Chingon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chingon/32/17645_2.png) [@Chingon](https://boards.straightdope.com/u/Chingon)\ **Post date:** [May 28, 2024, 12:39am UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/4 "2024-05-28T00:39:46Z")
997.048 grams > **[mass of 1000cc water - Wolfram|Alpha](https://www.wolframalpha.com/input/?i=mass%2Bof%2B1000cc%2Bwater)** > > Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [May 28, 2024, 4:52am UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/5 "2024-05-28T04:52:52Z")
> [@N9IWP](#): > > Depends on the concentration of deuterium, that can add a few femtograms… > **[Vienna Standard Mean Ocean Water](https://en.wikipedia.org/wiki/Vienna_Standard_Mean_Ocean_Water)** > > Vienna Standard Mean Ocean Water (VSMOW) is an isotopic standard for water, that is, a particular sample of water whose proportions of different isotopes of hydrogen and oxygen are accurately known. VSMOW is distilled from ocean water and does not contain salt or other impurities. Published and distributed by the Vienna-based International Atomic Energy Agency in 1968, the standard and its essentially identical successor, VSMOW2, continue to be used as a reference material. > Water samples made u... ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [May 28, 2024, 11:04am UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/6 "2024-05-28T11:04:04Z")
It’s not just deuterium – there are isotopes of oxygen, as well (ax the site DPRK cites makes clear). I’m sensitive to these things because my thesis work was on energy transfer among vibrational modes of cyanide ions, and there are four chief types of cyanide, depending upon the isotopes of carbon and nitrogen. It made a big difference in the spectra, because the masses affected the vibration frequencies. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [May 29, 2024, 12:39am UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/7 "2024-05-29T00:39:03Z")
Temperature has a bigger effect than any isotopic concerns. As the temperature rises, the density decreases, down to about 0.960 g/cm3 just before it boils (at 1 atm pressure). [![](https://www.engineeringtoolbox.com/docs/documents/595/Water_density_temp_pressure_F.jpg) ](https://www.engineeringtoolbox.com/docs/documents/595/Water_density_temp_pressure_F.jpg) ---
**Author:** ![Ignatz](https://avatars.discourse-cdn.com/v4/letter/i/3be4f8/32.png) [@Ignatz](https://boards.straightdope.com/u/Ignatz)\ **Post date:** [May 29, 2024, 12:44am UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/8 "2024-05-29T00:44:50Z")
The one I remember (and never had occasion to use) is 62.4 lbs/cubic foot ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [May 29, 2024, 3:29am UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/9 "2024-05-29T03:29:27Z")
I use the rule of thumb of 8.25 lb/gal ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [May 29, 2024, 7:08pm UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/10 "2024-05-29T19:08:59Z")
More on isotopes. The triple point of water depends on their proportions, and there’s some detail somewhere saying precise triple points must be measured using water averaged over “the seven seas”. Maybe this is from International Temperature Scale of 1990? Note the OP isn’t asking for e.g. a conversion factor, but in effect for a prediction of an experimental result. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 29, 2024, 8:31pm UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/11 "2024-05-29T20:31:44Z")
> [@CalMeacham](#): > > It made a big difference in the spectra, because the masses affected the vibration frequencies. Where by “big difference”, you mean “detectable, with sensitive enough instruments”? ---
**Author:** ![Peter\_Morris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peter_morris/32/359_2.png) [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)\ **Post date:** [May 29, 2024, 8:39pm UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/12 "2024-05-29T20:39:41Z")
> [@Napier](#): > > Note the OP isn’t asking for e.g. a conversion factor, but in effect for a prediction of an experimental result. Am I? It’s news to me. I was just curious whether the original definition of 1cc = 1g still works. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [May 30, 2024, 1:48am UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/13 "2024-05-30T01:48:50Z")
> [@Peter\_Morris](#): > > I was just curious whether the original definition of 1cc = 1g still works. It works perfectly for most definitions of ‘1’. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [May 30, 2024, 1:37pm UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/14 "2024-05-30T13:37:20Z")
> [@Peter\_Morris](#): > > Am I? It’s news to me. Sorry, my post was kind of insufficient. I didn’t assume you meant that knowingly or were thinking that specifically. My point was that “the original definition of 1cc = 1g” is an entirely different category from “the precise mass of exactly 1000 cc of water” which is no longer a thing “by current definitions”. It’s now a thing you can only measure, a thing that can no longer be asserted from definitions alone. There’s not an exact mass of 1000 cc of water. There are precision values, but they won’t match in all their digits and would be scattered according to experimental accuracy as well as definite known effects such as isotopic proportions, barometric pressure, purity, et cetera. ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [May 30, 2024, 1:53pm UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/15 "2024-05-30T13:53:18Z")
Looking at this as a purely mathematical exercise, is there a way to start with the assumption 1cc of water = 1g, use the redefinition of meter and kilogram to say that now 1cc of water = Xg? To avoid going into the weeds on isotopes, pressure and temperature, &c. treat my question as if it were: Before the redefinition of SI values, 1cc of vibranium was 1g under all conditions. After the redefinition, 1 cc of vibranium is how many grams? ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [May 30, 2024, 2:34pm UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/16 "2024-05-30T14:34:43Z")
> [@Napier](#): > > More on isotopes. The triple point of water depends on their proportions, and there’s some detail somewhere saying precise triple points must be measured using water averaged over “the seven seas”. Maybe this is from International Temperature Scale of 1990? Yea, [VSMOW2](https://analytical-reference-materials.iaea.org/vsmow2) (also mentioned in [Post 5](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/5)). Interesting tidbit about the triple point of water: it was defined to be 273.16 K (0.01 °C) between 1948 and 2019. Since 2019, it is no longer a defined temperature. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [May 30, 2024, 2:49pm UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/17 "2024-05-30T14:49:18Z")
> [@Saint\_Cad](#): > > is there a way to start with the assumption 1cc of water = 1g, use the redefinition of meter and kilogram to say that now 1cc of water = Xg? No. That’s the deeper change. Think of it this way. The density of water used to be a defined value. Now it’s not. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [May 31, 2024, 12:32pm UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/18 "2024-05-31T12:32:07Z")
> [@Chronos](#): > > Where by “big difference”, you mean “detectable, with sensitive enough instruments”? Well, yeah. But I was _using_ sensitive instruments. The differences stood out by a mile. ---
**Author:** ![kaylasdad99](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kaylasdad99/32/3398_2.png) [@kaylasdad99](https://boards.straightdope.com/u/kaylasdad99)\ **Post date:** [May 31, 2024, 4:41pm UTC](https://boards.straightdope.com/t/what-is-the-mass-of-water-be-precise/1002162/19 "2024-05-31T16:41:53Z")
_A pint’s a pound, the world around_. Leastways, that’s what my Mommy told me, and I’m not about to sit still while some egg-headed Poindexters call her a liar!