This is something I’ve been meaning to do for a *long* time, but kept finding excuses to put off. It uses the simplified cubic polynomial derived in Refractometer FG Results. Please visit that post for more information. You can also download a spreadsheet to track OG, FG, and more for multiple batches.

[...] (finally) written a PHP version of the basic FG calculation, so that people can use it without downloading the spreadsheet. [...]

Thanks for all the work with the Refractometer Calculator & putting a PHP version on your website. Very useful!

Jerry

[...] [...]

This is extremely helpful!! No more tedious math!! Thank you very much for putting this up!

Compared the last 5 brews I did with hydrometer and More beer refractometer program results. On all of them your OG specific gravity conversion from the brix reading was 2 (or so) sp gravity points lower than my hydrometer and the More beer values. These two were routinely within .5 sp gravity points. All the Fg calculations were spot on though!

Jack,

It sounds like the difference in OG you’re seeing could be due to the wort correction factor (1.04 by default). Are you applying a correction before using the MoreBeer sheet? If memory serves, it doesn’t have that capability.

At any rate, I’m glad it’s working out for you.

Sean

[...] various equations (good reading if you like that stuff). Probably the most accurate out there IMO. http://seanterrill.com/2012/01/06/refractometer-calculator/ GA_googleFillSlotWithSize("ca-pub-3927874040083090", "HomeBrewTalk_Forum_336x280_BTF", 336, 280); [...]

[...] I'm using Sean Terrill's refractometer FG calculator. Here's his website if your interested: http://seanterrill.com/2012/01/06/refractometer-calculator/ Anyway, with an OG of 12.86 brix and an FG of 7.06 brix according to Sean's calculator, the actual [...]

[...] an online calc for that or manual? There are several, most require a Brix reading. Here's one: http://seanterrill.com/2012/01/06/refractometer-calculator/ Your actual gravity is probably around 1.018 or 1.019 right now with the correction factor. Which [...]

[...] I just learned that it is always a good idea to check the correction factor that applies to your refractometer. A commonly accepted correction factor for converting a refractometer’s Brix reading to a hydrometer Plato reading is 1.04. I was always under the impression that the Brix reading has to be multiplied with this value, which works for me, but Sean Terril pointed out to me that the commonly accepted formula divides the Brix value by this correction factor to covert to a Plato reading. (Refractometer Calculator) [...]

Thanks for the calculator. Used it for my last two brews.

(while my hydrometer gently weeps)

Hi, thanks for the calculator. When a hydrometer sees me coming, it leaps screaming off the mantel to a glassy death.

I bought the refractometer two brews ago, and went through the old “how come it stopped fermenting?” when I took a reading I was expecting to be 1.010, but came out as 1.020. When the Internet told me how wrong I was to expect the device to make a reading in the presence of alcohol, I was already feeling guilty about the soon to be purchased and trashed hydrometer when I heard the show with James Spencer.

I don’t have a hydrometer :-) to check against, but the two low gravity beers I brewed in March seem to follow what I expected to get from OGs and observation when plugged into the calculator.

Hydrometers everywhere thank you,

Richard.

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Hi Sean, great work with all the calculations. How reliable do you feel this is?

I generally use a refractometer pre-boil and hydrometer post ferment as I haven’t felt I could trust the refractometers for measurements where alcohol was involved.

I was using your spreadsheet and keep track of my last 5 batches or so.

I currently have a Saison fermenting pre-boil was 15.2 brix, I measured the other day and I had 6.1brix, I also tested with my hydrometer and got 1.016sg.

Plugging the brix numbers in your calculator gives me a 1.008sg and approx 6.5% abv which is right where i want it. Putting the same numbers plus the hydrometer measurement in the spreadsheet gives me an abv of 5.5%.

Any theories?

Phillip,

The standard deviation for the 68 beers tested was 1.3 “points”. So if we make the assumption that those beers were a representative sample, then we can expect essentially all (99.7%) FGs to fall within 4 points of the predicted value. In reality, it was 97% for this data set, but that’s close enough.

So being 8 points off is highly unlikely. Have you calibrated the hydrometer and refractometer recently?

It could be that using a saison strain results in a large proportion of higher alcohols, or some other compound(s) that is/are throwing off the refractive index. If the correlation has given you good results when using other strains, I’d lean more towards that explanation.

Sorry I don’t have a definitive answer for you.

Sean

Hi Sean thanks for the reply, I went back and did a single point calibration of my hydrometer and my refractometer using distilled water at approx 68F. My refractometer was reading 0 which was good news however my hydrometer was reading between 3-4 points on the high side. This brings my readings inline with your calculations.

One more question, I put my OG in your calculator as 15.19 brix all the charts I’ve seen have this value in SG as 1.062, your calculator has it as 1.0594, where does that difference come from. I use the fermsoft grav brix chart for conversions mostly. http://www.fermsoft.com/gravbrix.php

Thanks again

Phillip.

Phillip,

Aha! This one’s easy. 15.2°Bx is in fact 1.062 SG, and if you were converting hydrometer readings it would be just that simple. Remember, though, that a refractometer doesn’t actually measure density – it measures the refractive index. That’s why a correction factor (1.04 by default) needs to be applied when using a refractometer with beer wort.

Sean

I’ve used your spread sheet for several batches. Currently I’m monitoring an open fermentation of a Russian Imperial Stout. OG was 25.3 Br, converting to ~1.103. I’m about 48 hours into fermentation and took a refractometer measurement for fun. It’s about 19 Br (fuzzy with yeast I’m sure, but the best fit for what I see). Entering that into your calculator and the spread sheet, the new cubic calculates 1.125 and the new linear calculates 1.043. Obviously the cubic is having a problem with this data (the 2 equations get close to each other in the 13-14 Br range), but how close is the linear calculation. It’s not that important right now, but it is interesting.

At this point, I wouldn’t assume that either correlation is giving good results. They won’t work below about 60% ADF, and you’re at the high end of the OG range as well.

[...] use this one: http://seanterrill.com/2012/01/06/refractometer-calculator/ Look here for more information about it: [...]

[...] from a post-fermentation refractometer reading. Some are better than others; my favorite is here: http://seanterrill.com/2012/01/06/refractometer-calculator/ But these are just estimates, and will likely be off of the true gravity by a few points. A good [...]

[...] instead of beer beer? In particular, do I need to change the "wort correction factor": http://seanterrill.com/2012/01/06/refractometer-calculator/ [...]

[...] http://seanterrill.com/2012/01/06/refractometer-calculator/ You can use another one to help average it out. My last batch started at 20.2 Brix, final Brix before bottling was 9.6. According to the calculator, estimated FG was 1.013, my hydro showed about 1.012+- [...]

[...] java app, android, etc. lol found a couple online: http://onebeer.net/refractometer.shtml http://seanterrill.com/2012/01/06/refractometer-calculator/ __________________ Fake it til you make [...]

can I put in gravity number instead of brix? – sorry kind of new to this….

thanks for the assistance.

The reason there isn’t an option to work in SG is because (as far as I know) there are no refractometers on the market with an accurate SG scale. If you want to do an approximate conversion, °Bx = 250 * (SG – 1). That will be significantly off for gravities over about 1.070, though. Here’s a lookup table using a better formula.

In the comment above you mention that there isn’t an option to work in SG because there are no refractometers on the market with an accurate SG scale…are you referring to the fact that most SG scales on refractometers are simply the brix reading multiplied by 4? The makers of this refractometer (http://www.ebay.com/itm/0-32-Brix-Wort-Beer-Refractometer-BREWfractometer-/370539814932) make a big deal about the fact that they’ve ‘corrected’ the SG scale so that it’s not simply the Brix scale multiplied by four. Would this be an accurate SG scale in your view?

Also, I noticed that if I change the “wort correction factor” in the box above and click calculate, the gravity numbers that it shows are correct, but the number in the “wort correction factor” box defaults back to 1.04…not a big deal, but a bit confusing when I was first doing the calculations. Anyway, great job on the calculator…thanks a lot.

I’m optimistic, but if the image in the eBay listing is representative, that model doesn’t appear to be any different from the others I’ve seen. If you look at 20°Bx, for example, that should correspond to 1.083 SG, but it appears to line up with ~1.077.

The behavior of the wort correction factor field is something that I also find frustrating. As far as I can figure out, there’s no way to populate it with a default value on the initial pageload without having it revert to the default on reloading. I’ll play around with it a bit more though, now that you’ve reminded me. Thanks.

Edit: Actually, the solution turned out to be fairly simple, and the WCF field should now have the behavior we both wanted. Thanks again for the reminder.

[...] luck with post fermentation Brix/S.G. calculators, but I haven't tried Sean Terrill's version See http://seanterrill.com/2012/01/06/refractometer-calculator/ I put your figures into that calculator, and it reported a F.G. of 1.0154 (only 2.6 points off, [...]

[...] to check gravity now that fermentation has begun as alcohol cause skewed readings (good one here: http://seanterrill.com/2012/01/06/refractometer-calculator/). There is really no need to transfer to secondary (bright tank) other than personal preference [...]

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[...] it for one type of beer, but it was way off for the next. Sean Terrill has the best calculator here. [...]

[...] timing, just went through this very topic in another post. The website to use seems to be.. http://seanterrill.com/2012/01/06/refractometer-calculator/ Here is the post we were discussing the drawbacks of using a refractometer for calculating beer [...]

[...] seems like a good time to pass on a handy calculator for approximating FG with a refractometer. http://seanterrill.com/2012/01/06/refractometer-calculator/ Sean's formula seems to be a lot more accurate than the morebeer or Promash ones. [...]

[...] Use this refractometer calculator instead of beersmith (link is below) . I find more accurate corrected values using this one. http://seanterrill.com/2012/01/06/refractometer-calculator/ [...]

[...] accurate calculator I have seen is this one: http://seanterrill.com/2012/01/06/refractometer-calculator/ Wy3711 could certainly bring 1.062 down to 1.002 with that grain bill and those mash parameters. [...]

[...] the alcohol affects refractometer readings. Check out the work done by Sean Terrill on his site: http://seanterrill.com/2012/01/06/refractometer-calculator/ he also gives a nice explanation of why the formulas and calculators are not accurate with [...]

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[...] for me. Two errors there. 1. I used an inaccurate calculator in the OP (MoreBeer spreadsheet). This one is better. 2. If you have the dual-scale Brix/SG refractometer from eBay, you can't trust the SG scale! My [...]

[...] easier done than explained http://seanterrill.com/2012/01/06/refractometer-calculator/ [...]

[...] say is more accurate than the old ones. I don't know because I have never tried it, but it is here: http://seanterrill.com/2012/01/06/refractometer-calculator/ With the exception of getting the FG, I see no use for a hydrometer. -a. __________________ [...]

[...] use the refractometer calculator on seanterrill.com to get an adjusted final gravity reading: http://seanterrill.com/2012/01/06/refractometer-calculator/ __________________ :: St. Pug [...]

[...] gravity was 13 brix and the final gravity around 5.8 brix. Plugging these numbers into Sean’s refractometer calculator (the best one out there), I get an OG of 1.0505 (12.5°P) and an FG of 1.0097 (2.49°P). The OG [...]