This is an enhanced version of my beer ABV calculator, which now works for both hydrometer and refractometer homebrewers. Please note that the calculations are a little different to those used in the previous version; this is intentional and this new calculator should be more accurate.
All the code is available on Github, along with details on the exact formulae being used and where they came from.
The Wort Correction Factor is generally required for refractometers which measure in Brix; unless you know better, it is best to leave it at the default value.
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ABV a little high? Brix reading 14.8 (initial) and 6.8 (final)
ABV= 131.25*(1.058-1.011) = 6.17 (calculator shows 6.35).
When I use OG =1+0,004*B3/1,04= 1.057 (I get the same FG of 1.011 through =1-0,00085683*B3/1,04+0,0034941*F3/1,04) I end up with ABV=6.07 (even lower).
The formula used by this calculator for the final ABV sum is a more complex version of “131.25 * difference”, which is intended to be slightly more accurate – especially for higher gravities. It does usually result in a slightly higher ABV than with the simpler formula.
The conversion from Brix to SG is also a lot more complex than “1 + 0.004 * Brix” (see the details on the Github page, linked above) – again, those formulae were chosen to be (hopefully) slightly more accurate.
Hey Pete! I was wondering how you were calculating your values from refractometer readings, as I just found the Sean Terrill site, which seemed pretty thorough. The github page didn’t actually say, so you forced me to read the code. 🙁
Just kidding, looks well written, but I did notice that your first coefficient in the RefractFinal formula is wrong. 0.004493 instead of 0.0044993. Probably not much of a difference, but…
Thanks again for the calculator!
You’re right – I’ve got some of the formulae listed on that page, but somehow I’ve failed to define (or attribute!) the final refractometer calculation. I shall amend that now.
And well done, you’ve spotted my deliberate typo 🙂
I’m trying to learn the calculations to take 2 brix/refractometer readings and get an ABV. These values may seem weird, but I’m working on a rum ferment… So starting Brix was 36. I checked it after 1 week and it was 24. Plugging those values into your calculator gives me a higher final gravity than my original gravity. How is this?
Corrected Original Gravity: 34.6 1.152
Calculated Final Gravity: 52.0 1.245
ABV: -.-%
I suspect the major problem is your high Brix values – the formulae used are only really valid for gravities up to around 1.1 (around the 25 Brix mark).
Actually, those high values will both generate invalid ABV *and* a faulty final gravity; while their probably are formulae out there that will cover a wider range, they’re pretty horrendous!
Thanks for the online calculator. Have checked yours vs actual sp. gravity readings & found it to be the most accurate. Much appreciated tool!
Can I use this calculator if I checked the first gravity with a refractometer and I want to check where the gravity is after fermenting for a while and has alcohol within the wine at this point? I’d hate to waste the wine using a hydrometer at this point.
You can – the calculator exists for this purpose, because it takes into account the effect the alcohol content has on the refractometer reading. The only caveat is that if you’re making wine rather than beer, the higher alcohol content may result in slight inaccuracies.
Thank you very much for the reply. That’s exactly what I’m doing too as the starting gravity was 1.118 for a little over 6 gallons and if all of the sugar has been eaten the alcohol should be around 17%. I’m fine with slight inaccuracies in alcohol, but I’m just trying to see if my wine is finished or if it has stalled. I’ll try it out and let you know how it goes. Thanks again!
This is amazing thanks! Measuring with a refractometer I had an OG of 1.047 (slightly off the 1.050 expected), I’ve been racking my brain as to why my beer seemed to get stuck at 1.024 SG after what seemed a fairly good fermentation period of two weeks with plenty of consistent bubbling.
Funnily enough, that’s exactly what started me looking for (and eventually writing) such a calculator 🙂
This is such a greatly appreciated tool. I’d been fretting over four different all-grain brews, ranging from a Pale Ale, two stouts and a Belgian quad…a backlog I cleared in just one crazy day. Two were familiar brews from my extract days, but two were new recipes. I was thrilled to get high conversion rates, and nail every single SG…but frustrated to see each brew petering-out well above their expected FGs.
I knew that a fermented beer would skew FG readings, but never realized just how much. Out of frustration, I compared “FG” of a newly-opened bottle of Black Butte to the FG of my clone attempt…yep, they matched. However, my calibrated refractometer still read well above what calculators said to expect…WTF…
That was until I punched SG/FG into your calculator, and suddenly my estimated and measured SG/FGs were all dead-on matches, for every single brew.
So thrilled that you’re sharing the source for this tool. Now to see if the folks at brewgr.com would be willing to incorporate your approach…
Thanks for making my day!
Pete, thanks for your effort and making this calculator available.
I’ve also found the Sean Terrill site, and I wonder why, when plugging in OG 18.5 Brix and FG 9 Brix, your calculations give essentially the same OG and GF in gravity (about 1.073 and 1.014) but your ABV is 8.17% while his is 7.6%. Big difference. I see your post on January 9, 2015 (I’m late to the party). Is the idea that your method of calculation is more accurate since this is a high gravity beer? Thanks!
Essentially, yes – the “simple” calculation more traditionally used by homebrewers (and the one, I think, that Sean uses) grows increasingly inaccurate as you reach higher ABVs.
I’m making a wine, and I use a refractometer. The kit I’m using says to measure each day until it gets between 1.040 and 1.050.
The original gravity was 1.093, and the first day the gravity lowered to 1.089, and the second day to 1.086.
Your refractometer calculator gives me a ‘corrected’ reading of 1.242 and 1.217 respectively. This can’t be right.
Fundamentally, the maths doesn’t quite work when you’re so early in the fermentation – it’s trying to correct for a bunch of alcohol that doesn’t yet exist.
I’d suggest leaving it alone for a week, by which time the fermentation will have calmed down and the figures will start to make more sense.
[…] before fermentation and then again after fermentation. Based on the readings you can use an ABV calculator to determine the amount of sugars consumed, and therefore the amount of alcohol produced. The […]
How accurate is this formula for mead and high alc wines SG 1.140+?
It grows increasingly inaccurate for higher SGs, because of the nature of the mathematical approximation.
Hey!
I just found your calculator on the internet and your sound right.
Thank you!
This is just what I was looking for after discovering that my final gravity (FG) reading on the refractometer did not match the hydrometer. I discovered that this is due to the alcohol in the brew. I used your calculator to make a chart for corrected FG and am good to go. I am verifying the correction with my hydrometer, but so far it is spot on.
Hi.
Thanks for this quite accurate calculator.
It´s always right on the spot or +-0.001.
(I dont know why, but its most accurate if I measure with brix even if I look at the final numbers in SG.)
Have you ever considered about making this to on app (for android)?
It could be wery simple app.
The benefit would be that its always usable (internetconnection or not)
and that it would could save your previous numbers (specially correction factor) so if you close tha app and open it again, the calculations would still be there waiting for you.
Second this idea, would love this in a phone app!
Question: is your calculator accurate for cider too? Thanks.
I can’t see why it wouldn’t work!
If FG “specific gravity” is in subzero say 0.995 calculator gives error
Yes; if you’ve ended up with a FG of below 1 then something strange is going on and I wouldn’t expect the calculator to come up with a very useful answer.
Something is off in this. If I put in a OG of 1.066 and then check soon after the start of fermentation, and put in FG of 1.064, it tells me that my actual SG is 1.085. I saw your reply to an earlier question like this that the math is “Accounting for alcohol that isn’t there yet”, but that isn’t how the math should work. It should be only accounting for the alcohol that IS there. And that isn’t much when my SG has only dropped by 0.002. In fact entering a FG = OG = 1.066 says my SG is 1.093 which is a boundary condition check you need to handle.
The trouble is that the calculation is very much a ‘best fit’ to a complex curve and at the extremes (either early in the fermentation, or at high strengths) it becomes increasingly inaccurate.
If your current gravity is only 0.002 below the start, then it’s presumably still actively and visibly fermenting so I’m not sure what value you get from trying to calculate what will be a very transitory ABV.
Do I need the WCF at refractometer readings for wine too? Before fermentation, like for beer.
I’m honestly not sure; WCF is used with beer because refractometers are generally calibrated for ‘purer’ sugar solutions – I would imagine a correction would be needed for pre-fermented wine too, although it may not be the same as for beer.
To be honest, I’d be inclined to either leave it as set, or set it to 1; it’s a pretty minor calibration.
Do you have an idea on my request regarding the WCF for wine using refractometer?
thank you.
Hi. Thanks for the awesome calculator.
Any idea how to embed the refractometer-calculator to my google sheet file?
The actual calculations are (reasonably well) described in the linked code. I’ve never done anything fancy in Google Sheets, so I’m afraid I can’t help you there!
What’s the difference between the measured original gravity and the corrected gravity if there is no alcohol present? Using my digital refrac, which measures in Brix, I get a OG of 12.4 – why would does ‘correct’ it to 11.9?
Fundamentally, because refractometers are (generally) calibrated to sugar water, which has a different density to your wort. This will vary somewhat from instrument to instrument, but 1.04 correction factor seems to be the conventional wisdom for beer brewing.
Thanks for the reply. Is the OG input supposed to be entered as Brix or Plato?
Using my digi refrac – my OG is 12.9P (or 12.4 Brix)
They are closely related, and *some* sources (but by no means all) will tell you that Plato effectively already has a wort factor applied(1) – so, I’d be inclined to either use Brix and leave the correction factor at 1.04, or Plato and set it to 1.
(1) it’s actually more complicated than that, but there is some logic to it.