Hydrometer Issues?

Just took a reading of a batch of Irish Red and the abv is 2.0... Just out of curiosity, I opened a bottle of Sam Adams and it read around 3.0, when the actual abv is 4.75%?? I'm assuming a new hydrometer is needed, but not sure. Any suggestions?

That's not how you calculate abv....nor can you get a good reading of gravity on a carbonated beer.

For one thing we don't use the "Potential alcohol scale" on the triple scale hydrometer, that is only used in distillation of whiskey.

To calculate abv you take an original gravity reading on brew day, then a final gravity reading (I usually take mine a month after I pitched yeast on bottling day)

The calculation for ABV is Og-fg X 131 = %Abv.

To see if you need a new hyrometer you take a reading on distilled water and it should read 1.000 in distilled water.

Revvy beat me to it.

I was going to ask what the OG of Sam Adams is.

The hydrometer doesn't give ABV on a single reading, short of brewing wine or other drinks that will ferment to 1.000 or damn close. You have to take the original and final gravity of the beer to find your reading.

So just trying it a fermented beer will give you a low reading, if you knew the starting gravity of said brew you could determine the ABV almost exactly.