Refractomemter Scale question - help

[brettg20]

Hey all, quick question about the scale on refractometers. I am about to purchase one and after doing research have learned that by multiplying the brix scale by 4 you roughly get the SG. For example if you get a brix reading of 10, SG is roughly 1.040 and so on. But then why does the scale not line up Brix 10 to SG 1.040 and so on....it seems that the SG numbers are higher on the built in scale on the refractometer, but in reality it should be the other way??

Morebeer.com states "Take a Brix reading of 10, multiply by 4, and you get a SG reading of 1.040 - the accurate SG reading is 1.041. Take a Brix reading of 20, multiply by 4, and you get 1.080 - the accurate conversion is 1.084." But if you look at the picture http://www.northernbrewer.com/brewing/brix-specific-gravity-refractometer-w-atc.html of the scale why is 1.080 not lined up with 20 Brix etc??

 

[Krrazy]

I believe the scales don't line up because the multiplication by 4 is not the exact conversion formula but a close approximation that works at lower gravities. They talk about that a bit in the More Beer description. If you do some searching you'll see that that formula is a bit more complicated but I think the x4 rule gets you close enough in most cases. Doing the math yourself or using one of the spreadsheets out there will give you the exact conversion. In the 10 Brix example, I think the exact conversion would be 1.03979.....close enough to 1.040.

 

[malkore]

I use online calculators, because the x4 method is a rough estimate only.

 

[rico567]

Yeah, if I want my OG calculation, post-boil & all, then I might consult an online calculator. For everything prior to that, just multiplying X4 mentally works for me.

 

[Bobby_M]

It's more like brix x 4 - 1 or 2.