Just too different measuring scale. Just like Celcius and Farenheight for temperature. THere are numerous conversion scales out there. You can down load calculators or charts. Almost every brewing book I have has a chart in it as well.
Here is a text clip from our sister site Homebrew Talk's Wiki Page on the subject.
Brix can be approximately converted to specific gravity (SG) by a simple equation:
SG = 1 +(0.004 x Brix)
Most people just remember the multiply by four rule. Take the Brix reading, multiply by 4 and this will give you specific gravity in “gravity points.” For example, if you read 11 Brix, multiplying that by 4 yields 44, which corresponds to a specific gravity of 1.044.
Well if you want to know the sugar contend of a grape / fruit before picking all you need is to squeeze a grape over the refractometer and you have it
SG is measured when you have a liquid.
Both are interchangeable as stated above.
I have a three scale hydrometer also.
It gives SG, approximate sugar content and potential alcohol percentage.
Now the SG scale is correct. That can easily be tested.
The sugar and potential alcohol content are way off....... More as 10% !!!!!
So I had an e-mail conversation with the technical department of the hydrometer manufacturer and their answer was hilarious. Although they admitted the fault.............
Major story coming up on my web-log in due time
I therefore suggest stick to the SG scale and test that (by dissolving a known quantity of sugar in a known quantity of water) and be very carefull with the other scales on your meter.....
We use Brix hydrometers in the lab at the winery. Very easy to calcuate the amount of % sugar is in the juice or wine as it progresses. 22.5 brix tranlatles to rule of thumb of 22.5 % sugars. Nice point to start frementing white wines. When wine is totally dry I switch to a hydrometer I have that is 5 to 0 then -0 to -5 brix. at -1.7 it is generally dry.