If a person wanted to have beer or other alcoholic beverage tested for ABV, where would one have that done? I always use online ABV calculators, which are generally accurate enough for beer I’m not selling, but I strongly suspect that their accuracy drops off as the ABV goes up. They seem to be just a linear calculation that doesn’t take into account the gravity lowering effect of the alcohol. I don’t “need” to know the actual ABV on anything I brew, but am curious about a few of my bigger beers.
There is the boil off method. I’ve never actually tried it myself. This post is about wine, but from the description I don’t see why it wouldn’t work for beer.
https://www.winemakingtalk.com/threads/determining-abv-after-wine-is-made.16259/