A hydrometer is used to measure the amount of sugar that is contained in a liquid. For home brewers, by measuring the sugar content of our wort at the beginning and at the end of fermentation we can calculate the amount of alcohol in our finished beer as well as get a sense of how well our yeast have performed.

How Does A Hydrometer Work?:
A Hydrometer works on the principle that the more sugar there is in a solution, the denser it will be. The denser a sample is, the less far a hydrometer will sink down into it.

density is affected by temperature: cooler liquids are more dense than warmer ones. Hydrometers take this into account and have been calibrated to give an accurate reading at a specific temperature noted on the hydrometer scale (usually 60-70 F, or "room temp"). You will need to make sure your sample is at this temperature to get an accurate reading.

How To Use a Hydrometer:
  1. Add your sample to the hydrometer jar (sample holder). Make sure the temperature is in the recommended range as per your specific hydrometer. Use enough sample to make sure the hydrometer does not touch the bottom of the sample jar.
  2. Place the hydrometer into the liquid and allow it to settle (maybe do this over a sink in case of overflow!). Take care that the hydrometer does not touch the sides of the hydrometer jar or it will throw the reading off.
  3. Where the liquid intersects the scale is your reading. Important: The liquid will lift up a little where it touches the wall of the sample jar and the hydrometer itself. This curve in the liquid surface is called a meniscus. Do not take your reading at the top of the lifted edge. Rather, take your reading at the lowest level of the liquid surface, the bottom of the "meniscus", and project this onto the scale.