Measuring Specific Gravity without a Hydrometer

Basically, I'm lazy and cheap and haven't bought a hydrometer yet. It's also partly because I already have the stuff I need to measure the density of liquids. And I don't brew very often. If you're not familiar with brewing, measuring the density of liquids is useful for estimating the resultant alcohol concentration after brewing. Instead of buying a hydrometer to do this I just use a scale and a graduated cylinder. Admittedly, this is nowhere near as convenient as a hydrometer. In fact it's pretty fickle, and introduces more error by requiring two measuring instruments. But it seems decently accurate. My last cider measured in at 16% ABV, and it tasted and felt like it was 16%...

As an example here I have measured out 10ml off water in a small graduated cylinder. I don't use the tare function because it shuts off after like 20 seconds or something super annoyingly short. You can see below I have the weight before and after filling the cylinder. It's .01 grams under what it should be, so obviously this isn't perfect. But it's good enough for me. If you haven't figured it out, the density (or specific gravity) is the mass over the volume. To use this to find the alcohol concentration of a fermented beverage, measure the specific gravity before fermentation, and after fermentation. Subtract the ending SG from the starting SG and multiply it by 131. This is the approximate ABV! Basically you are measuring the amount of sugar that was converted into alcohol by the yeast. The sugar provided by your mash or wort increases the density of the water, but once its converted into alcohol, that lowers the density because alcohol is less dense than water. 131 is an approximate conversion factor. I don't know who figured that out or how.

If you forgot to measure the specific density before starting your brew, or your realized that the sugar you added at bottling for carbonation changed the density (like I did) then there are charts and smart people out there online that can help you estimate how much density different types of sugars will add to a brew. I've done this before. It introduces another vector for error, but I do that a lot apparently.