Updated: 5/29/2024

In days of yore, refractometers were considered a pre-fermentation only tool.  That’s because the alcohol present after fermentation begins throws off refractometer readings.  That was until people starting figuring out that it was possible to reasonably estimate specific gravity after fermentation has begun.  The first such calculations that I became aware of were from MoreBeer.  Check the documents tab on this product page to see their spreadsheet.

Since that time, additional work has been done to refine these calculations.  One such body of work belongs to Sean Terrill.  Sean is a smart guy.  Like nuclear engineer kind of smart.  Sean did a good bit of work on the subject and came up with an even more accurate formula for estimating specific gravity after fermentation is begun.

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aichose Brix Refractometer with ATC, Dual Scale - Specific Gravity & Brix, Hydrometer in Wine Making and Beer Brewing, Homebrew Kit

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Beer Wort Refractometer for Homebrewing Beer, Dual Scale Specific Gravity 1.000-1.130 and Brix 0~32%, Beerbrewing Refractometer Hydrometer with (ATC) Autoction Temperature Compensation

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Brix Refractometer with ATC, Dual Scale - Specific Gravity & Brix, Hydrometer in Wine Making and Beer Brewing, Homebrew Kit

Brix Refractometer with ATC - Tiaoyeer Digital Handheld Refractometer for Beer Wine Brewing, Dual Scale-Specific Gravity 1.000-1.130 and Brix 0-32%

$17.99

Anpro Brix Refractometer with ATC,Refractometer for win Moisture, Brix and Baume,Dual Scale-Specific Gravity 1.000-1.130 and Brix 0-32%, for Wine Making,Beer Brewing,Maple Syrup,Molasses

Aichose Brix Refractometer for Measuring Sugar Content in Brewing, Cooking and Food Indurstry.Dual Scale: Brix of 0-32% and Corresponding Specific Gravity

Ade Advanced Optics BCBI9177 Beer Wort and Wine Refractometer, Dual Scale - Specific Gravity 1.000-1.120 and Brix 0-32%, Replaces Homebrew Hydrometer (Aluminum)

$28.99

Digital Brix Refractometer Flagfront brix Meter Refractometer Automatic Temperature Compensation Brix Refractometer Range 0-55%，±0.1% Precision for Fruit Juice Coffee

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MILWAUKEE'S Instruments MA871 Digital Brix Refractometer, Range 0-85%

$149.40 -$30.46 $118.94

Atago 3810 PAL-1 Digital Hand Held Pocket Refractometer, 0.0 - 53.0% Brix Measurement Range

$250.22

DiFluid Digital Brix Refractometer & Concentration Meter, 0-55% Range, ±0.1% Precision, Waterproof & Rechargeable, for Beer, Wine, Fruit & More

To do this you need: A pre-fermentation refractometer reading, a current refractometer reading and a spreadsheet or online calculator.

Sean has kindly made his findings available to the homebrewing community.  You can use his easy to use refractometer calculator or his spreadsheet (available on the calculator page).  He also makes it available for others to use with proper citation.  For example, my Brewing Spreadsheets [Brewing Spreadsheet | Small Batch BIAB Spreadsheet | BIAB Brew Day Spreadsheet] all contain Sean’s formula.  Thank you to Sean Terrill for your work on this subject and for making this available to homebrewers!

Need More?

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My Brewing Spreadsheet Feature’s Sean’s Calculator!

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Make sure the components you use are compatible and rated for your intended application.  Contact manufacturer with questions about suitability or a specific application.  Always read and follow manufacturer directions. tag:lnksfxd top:strefractcalc tag:tpr