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Converting baumé to Concentration

Q. Having had multiple years of chemistry in my education, this is the first time I have come across this system of measurement. Reading the explanation of its calculation begs the question, why has this arcane system been adhered to for so long? Obviously there is some unique practical utility in its use that is not obvious to me ... something like using sand timers and sundials for analytical chemistry.

Howard Fraley
Doctor, believe it or not. - Akron, Ohio, USA
September 22, 2023

Basically it's the same reason a handful of (very significant) countries are still using customary/imperial/inch-pound units instead of the metric system: inertia. If something works "well enough", and the alternative is superior but not drastically so, especially if the transition inherently must be quick or otherwise difficult (either from a technical perspective or merely a "relearning" aspect), it often does take a government decree to get people (and/or industry) to switch away from what they've been using "forever".

I rather note that degrees Baumé especially, is not used by any serious modern chemist, but seems to be mostly found in industrial commodity chemical sales. You're never going to get the chemical industry to change the concentration of the acids they sell, because then everybody would have to adjust their recipes. The fact that these concentrations were originally defined via an archaic unit system is for all practical purposes a historical footnote, but just like it's easier to say you're buying "a gallon" of milk than "a 3.79 liter bottle" of milk, it's easier to say that nitric acid is sold at "42° Baumé" than "67.18%". Though at this point, the bottle of milk does typically mention "3.79 L" on it, and nitric acid documents do typically mention "67.18%".

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
stellar solutions banner
September 25, 2023

⇩ Related postings, oldest first ⇩

Q. I have hydrochloric acid that is labeled as being 22°Bé which I have found is Baumé. How do I know what concentration this solution is so that I can make a 5% HCl solution? Thanks.

Kristen MacKay
research assistant - Kelowna, British Columbia, Canada

A. Someone will probably do your work for you, but you need to find it for yourself.
Lange's Handbook of Chemistry [adv: on Amazon, AbeBooks, or eBay (adv.)] ,
• The CRC Handbook of Chemistry & Physics [adv: on Amazon & AbeBooks & eBay (adv.)] ,
• Perry's Chemical Engineers Handbook [adv: suggestions on Amazon, AbeBooks, or eBay (adv.)]
and a few others all have conversion charts. The next problem is 5% of what? Many would equate this to 5% by volume of reagent quality HCl, which is 37% by weight hydrogen chloride in water. Also is it 5% by volume (of what) or 5% by weight (of what)? If this is for a chemical analysis, there will be a listing (in the front or the back of your analysis source book) of the strength and or purity of each chemical.

James Watts
- Navarre, Florida

A. That was a very good and educative reply by James Watt; but it seems (and I'm probably wrong) that only HCl's strength is measured in Baumé scale?

freeman newton portrait
Freeman Newton [deceased]
R.I.P. old friend (It is our sad duty to
advise that Freeman passed away 4/21/12)

A. Actually, the concentration of a lot of acids (HNO3, H2SO4, HCl, etc.) are measured in degrees Baumé (heaviness scale).

James Totter
James Totter, CEF
- Tallahassee, Florida

A. Nitric acid is also sold by baumé. Sulfuric is frequently sold by % or by specific gravity, but I bet someone sells it by baumé. Reagent grade HCl (muriatic) is sold by %.

James Watts
- Navarre, Florida

Baumé scale

A. Hi. Just to complete this sub-thread before moving on, Baumé is an old scale invented by Antoine Baumé whereby the strength of acids is expressed by their relative weight. According to Wikipedia , the relationship between specific gravity and baumé at 60 °F is:

S.G. = 145 / (145 - °baumé)

Some references use 144 rather than 145. But in any case, since the only unit in the formula is specific gravity, the units for baumé are the same as for specific gravity, which is to say it's a pure number not dependent upon metric system vs. inch-pound system.


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

Q. Please tell me how to convert commercial grade HCl which I am told by the vendor is 32-33% to 10% concentration. How do I convert 32% of this acid to 10% HCl. Currently what I am doing is taking 79 ml of HCl and 21 ml of water.
My formulas is as follows.

32% HCl contains 68% water
10% HCl contains 68/32*10 = 21 ml water.
Is this correct?

Thanks & sincerely awaiting.

Dr. W.A.C
- RWP, Pakistan

Ed. note: Welcome! Feel free to visit anonymously! But our 35-year legacy of warm aloha is incompatible with anonymity; please only post with your full real name.

A. Hi. That doesn't sound right to me, Doc. But I think it's far easier to think in terms of the amount of acid rather than the amount of water ...

You apparently want 100 ml of solution for your addition or analysis, and you want it to contain 10% (by volume) of "pure" HCl. So you want your 100 ml of solution to contain 10 ml of HCl because 100 x 10% = 10 ml.

If the starting solution is 32% (by volume) HCl, each ml of that solution obviously contains .32 ml of "pure" HCl. To obtain 10 ml of "pure" HCl, you would require 10/.32 = 31.25 ml of your 32% solution -- which you would add to 68.75 ml (100 ml total - 31.25 ml) of pure water to reach your 100 ml of 10% strength.


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

Q. Hello --

I new in the world of metal finishing, and I notice that some specifications specify a bath concentration in volume of the acids, but these values refer to a volume of commercial acids like 42°Bé Nitric and 70% HF. So, what is the commercial concentration of HCl or muriatic acid?


Yohands Rey
aerospace - Mexico
February 16, 2009

A. Typical "commercial grade" HCl is 32-33%. In my experience, when plating facilities talk about xx% concentration in an acid bath, they mean xx% of the commercial grade acid. For example, a "25% muriatic bath" is 1 part of 32-33% HCl and 3 parts water.

Matt Poppe
finishing shop - Minneapolis, Minnesota, USA

Q. I have noted the concentration of HCl as listed does not discern between the actual concentration of HCl or the diluted (industrial strength) HCl. As an R&D chemist, I tend to think "actual" concentrations even when starting with dilute solutions. I would appreciate if someone could clarify this for me as I am trying to establish a testing protocol and seem to be floundering. Please advise!

Denise Cooper
- Piedmont, South Carolina, USA
December 18, 2012

A. Hi Denise. We appended your inquiry to a thread which explains some rationale for using 32-33% commercial strength HCl as the basis for your calculations, and which implies that expressing concentration by volume rather than weight offers practical advantages.

As additional justification, I would add that HCl is not a liquid, but a gas dissolved in water, so higher concentrations than that aren't practical anyway and would take us into rather "artificial" calculations. I'd say the answer is to adopt the convention that Matt says is the most common one (concentration by volume, measured against the 32-33% commercial standard). But I'm not a chemist :-)


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

A. Chemists tend to like concentration in terms of moles per liter, or at least some mass per volume that can be converted to moles per liter. Most useful things that chemists tend to think about only operate in units like this. We always keep in mind that a concentrate solution is already some quantity of material in water.

Manufacturers tend to like concentration in terms of volume percent, volume ratio, mass percent, or some other simple measurement that can be used by workers who possibly have forgotten everything they learned in the one semester of chemistry they ever had in their life. Concentrate solutions are viewed as mystery stuff to be mixed in some set quantity with another set quantity of water.

So yes, a chemist in the manufacturing field must be ready to use whatever conversion factors are available to move back and forth between units that are useful for chemical calculations and units that are useful on the factory floor. The major thing is to know your audience, and to know what audience a set of mixing instructions was meant for.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
stellar solutions banner

Q. I am trying to figure out how much nitric acid and sodium dichromate go into a 130 gallon bath for AMS2700 D nitric acid passivation type 2.
It takes 20 to 25% by volume of nitric acid,
and 2 to 3% by weight of sodium dichromate.

Ryan Thompson
- Vidalia, Georgia
November 21, 2013

A. Hi Ryan, For a 25% v/v nitric acid solution you will need 130/4 = 32.5 litres of acid. When you say 2-3% m/v dichromate then that is the equivalent to 20-30 grammes per litre.
So 1 US gallon = 3.78 litres, Then 130 x 3.78 = 491 litres of liquid volume.
491 x 30 g/l = 14730 g or 14.7 kg of dichromate.
Hope this helps and good luck.

Mark Lees
Aerospace - Isle of Man, Great Britain

A. You would find life much simpler if you were to work in grammes per litre.
You avoid problems like an imperial gallon being 4.2 litres and an American gallon 3.8 L
Ounces - Is that Avoirdupois or Troy as used for gold and silver? Or could it be the apothecary or perhaps the fluid ounce?
Did you know that there are two baumé scales? Light baumé is for solvents and heavy baumé for aqueous solutions. The problem is that both hydrometers look similar. Pick up the wrong one and----!

I wonder how many mistakes these archaic units cause each year.

geoff smith
Geoff Smith
Hampshire, England

thumbs up signHi Geoff. As an American engineer I appreciate the dichotomy there! We've always like sticking with our own system because if we can make others struggle with what we're used to, instead of us struggling with what they are used to, it gives us a leg up :-)

On the other hand, I can't tell you how many times in my career I've seen construction errors because of switching back and forth between inches and feet & inches. A foot is 12 inches, but is accidentally converted to 10 inches constantly --

"6 foot 2, eyes of blue, coochy coochy coochy coo ..."


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

A. Okay. This is not overly complex math, but it's been a long time since math class for some of us. I'll stick with Imperial units to keep it simple, there's nothing here that is particularly made easier by converting to metric.

130 * .20 = 26
130 * .25 = 32.5

So you need your 130 gallons of bath to include between 26 and 32.5 gallons of concentrated nitric acid.

130 gallons of 20-25% nitric acid will weigh a little more than 130 gallons of water does. We can decide to ignore that and just go with the density of water 8.35 lb/gal, in which case

8.35 * 130 = 1085.5
1085.5 * 3 / 97 = 33.6
1085.5 * 2 / 98 = 22.2

Add between 22.2 and 33.6 lbs of sodium dichromate. Or weigh out a known quantity of the 20-25% nitric solution to get the correct density and run the math using that.

As an aside, if you ever want to get away from using such nasty chemicals, see if you would be allowed to use the "Method 2" passivation in 2700.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
stellar solutions banner

Q. Excuse me sir I need answer for question about the number of baume scale 140 in formula and 130. where did they come from and what's the meaning of this number?
And I will be very thankful if you answer me.

haider saadoon
chemical - baghdad. iraq
September 8, 2021

A. Hi Haider. The number "140" does not appear on this page ... maybe you mean 145? Antoine Baumé invented his scale, which is:
Specific Gravity = 145 / (145 - °baumé).
The number 145 was perhaps arbitrary, but once he chose it we must honor it as the conversion between specific gravity and the baumé scale

The number "130" in Ray's answer was just in response to Ryan Thompson's 130 gallon tank.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

Q. Dear Sir,
My question is why do we calculate sulfuric acid based on weight like 200 gm/liter -- why not volume based? And how should we decide which chemical has to be calculated on weight basis and which one on volume basis?

Aijazullah Tajir
- Abu Dhabi, UAE
January 20, 2014

A. Hello Aijazulla,
If I understand your question correctly, you probably know sulfuric acid is supplied in various concentrations. battery acid [affil links] is around 35%; 50% and 98% used in the plating industry, as well as other industries. Purity is also an important factor when using sulfuric. This is why there are different grades of acid available, i.e. - PC, electronic, and reagent grades are some examples. Also sulfuric acid absorbs water from the air, especially at high concentrations. A simple lab titration to determine concentration is the norm for proper analysis. Determination by volume alone would not be accurate. Hope this answers your question.

Mark Baker
process engineer - Malone, New York

How do I calculate weight percent of a plating solution?

Q. I have been going through our records and tank makeups, some tanks are made up in percent by volume, others in percent by weight. I apologize for being a bit rusty, but I guess this is what happens when you just rely on the paper instead of doing the math.

I understand the math to make up a concentration when it is percent by volume, that is easy. My question is how do I make up a percent by weight tank? For example, we make up our anodizing tanks at 15% by weight sulfuric acid, I know that equates to 9.3% by volume. But I only know that because our chemical supplier has told me so. What is the mathematical equation I would use to figure out (verify) these numbers? I need to check the numbers on a variety of tanks and chemicals.


Carson Sewell
Metal finishing - Southington Connecticut
July 2, 2014

A. There may be a simpler way, but this is how I do it.

First, on the internet or a chemical handbook, find the specific gravity (SG) of a 15%, by weight, sulfuric acid solution. This will vary depending on the temperature. Many of the charts are based on 20 °C and, since that is close to room temperature (68 °F), that is what I would use. I know of no formula that will directly give the relationship between the concentration by weight and the specific gravity. The easiest way is to find and use a chart.

According to one chart I found, the SG of 15%(w/w) sulfuric acid at 20 °C is 1.102g/cc. Therefore, one liter would weigh 1.102 X 1000 = 1102g.

At 15%, there would be 1102 X .15 = 165.3 grams of sulfuric in one liter.

One mole of sulfuric weighs about 98 g. Therefore, there is 165.3/98 = 1.6867 moles of sulfuric in one liter of 15%.

Assuming the concentrated sulfuric you are using is 96%, a liter contains 18 moles. Therefore, to make up a 15%, by weight, solution would require 1.6867/18 = .0937, or 9.37% of 96% sulfuric, by volume.

Chris Owen
- Nevada, Missouri, USA

Q. Was trying to see if anyone could help concerning making a 5% dilute solution using HCl. I will be using 1000 gallons of water to chemically clean some equipment and was curious to know if someone had an idea on how many gallons of HCl would be needed, or an easy formula to figure it out on my own. Thanks.

michael martinez
- texas city Texas U.S.A.
October 3, 2014

A. Hi Michael. You don't say what the starting concentration of your HCl is (it's not 100%). Step 1 is to find out the concentration of the acid you're starting with. Step 2 is to study the MSDS sheet and be sure you are properly trained, and have the right PPE (personal protective equipment) to do the job safely. Then step 3 can be to prepare the diluted solution per the calculation shown above in my response of December 2012 to Dr. W.A.C. of Pakistan.

That is:
- If you want 1000 gallons of 5% HCl, you'll want the 1000 gallons to contain 50 gallons of "pure" HCl (5% of 1000 gallons).
- If you start with 32% HCl, each gallon will contain .32 gallons of "pure" HCl, so to get 50 gallons you'll need to add 50/.32 = 156.25 gallons of 32% HCl.
- Since you want to end up with 1000 gallons of solution, and you'll be adding 156.25 gallons of the 32% HCl, you need to start with 1000-156.25 = 843.75 gallons of water.

"Do as you oughta, add acid to water". Best of luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

A. Ted .. you are giving a good help to this site.
Regarding the chemical formula for dilution of any concentrated solution :
Concentration * Volume (of conc. solution ) = Concentration * volume (of final dilute solution )
(concentration could be expressed in % or moles or normality )
As a rule of dilution, Concentrated solution should be added to the dilute or to water in order to absorb the heat of dilution.

Yehia Selim
Pharos University in Alexandria - Alexandria , Egypt.

A. Reading through this whole very informative thread (plenty of good humour about the US vs Metric measurements too; I've got a copy of Josh Bazell's 'How To Use The Metric System' taped to my lab door as a warning and have shooed people out with the instructions to read it, come back in, and talk to me in metric)...
I have one very simple thing to add to the conversation. If you've got chemicals, you've got Safety Data Sheets (aka MSDS) too. If you don't, hurry up and get them! Anything you buy in baumé will be listed in %w/v somewhere in there, and you can use that as a starting number for dilution calculations.

Rachel Mackintosh
- Greenfield, Vermont
June 2016

Great tip, Rachel. Thanks!

I couldn't find your ref with google, but did find
which seemed to at least allude to his book "Wild Thing" and its metromedy. My favorite line in the comments was "Jet fuel can't boil American water" -- which was probably only funny to me and whoever wrote it.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

Ed. note Sept. 2023: Don't go to that website! That's a problem with links: bad actors buy up expired links :-(

"Wild Thing"

on AbeBooks

or eBay on


(affil links)

Indeed from 'Wild Thing'. Here it is:

"In metric, one milliliter of water occupies one cubic centimeter, weighs one gram, and requires one calorie of energy to heat up by one degree Celsius, which is one percent of the difference between its freezing point and its boiling point. An amount of hydrogen weighing the same amount has exactly one mole of atoms in it. Whereas in the American system, the answer to How much energy does it take to boil a room-temperature gallon of water? is Go f*** yourself, because you can't directly relate any of those quantities."
-Josh Bazell

Rachel Mackintosh
- Greenfield, Vermont

Q. Neutralization of crude edible oil using NaOH depends on pH value of the oil. I am not a technical guy - pH <5 is recommended to be neutralized by 11 Bé. How can I convert 11 Be into percent of weight of the crude oil?

Chikaiko Chadzunda
- Lilongwe, Malawi
August 30, 2016

A. Hi Chikaiko. Alkalinity & acidity are not the same thing as pH, so your theory that you can determine the required amount of NaOH from a pH reading may be flawed from the start. But you never do a neutralization like this by theory anyway. You always do a beaker test / lab titration and then scale things up, so why drive yourself crazy with conversions from the defective broken baumé scale? Instead, do a lab neutralization, measuring the quantity of "11 Baumé" required, and proportion things upward. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

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