ibu measurements

Can anyone tell me the difference between tinseth, rager and garetz? The brew software I use always asks which one I prefer when building a recipe. I just know that Sam Adams is 30 ibu and that's about as bitter as I like. Thanks

They are just different ways of estimating the actual IBUs in a beer, which is an actual, measurable thing (but expensive to actually measure, so we estimate). Tinseth is the most popular, I think, and probably the most accurate for our beers. Garetz is pretty old- not used by many people.

Once you start brewing it doesn't matter so long as you don't switch systems. When you brew a beer of a certain gravity at a certain indicated IBU by your chosen measuring convention, it becomes comparable to itself from then on.

I have no idea what the Beersmith default is for IBUs, I never touched it (I think Tinseth?). But I know exactly how subjectively bitter 40 IBUs indicated in the software is for a ~1.060 grav APA. I know 88 IBU is about right (for me) for my 1.080 OG Double IPA. My wheats can handle up to about 20 indicated IBUs before the hop bitterness is noticeable. I pay as much attention to the IBU/SG ratio as raw IBU numbers. Brew an Imperial Stout at just 30 IBUs and it will likely be cloyingly sweet. A Blonde Ale would be too bitter (subjectively of course).

Ok. Cool that clears things up for me. I was under the assumption that ibu's were the same on all beers. I never thought about the relation between sg and ibu. I guess its just a matter of finding what u like in the different styles of beer. Thanks