Understanding how to to read a Hydrometer can be confusing due to the fact that there are an array of numbers, scales and colors pasted all over a small area of tubular glass. But a Hydrometer is an essential tool when making wine or beer, and understanding how to read it properly will ensure your homebrewing success! The most common reading you will take with a hydrometer is a specific gravity reading. This reading is based on how your liquid compares to the specific gravity of water. Water will measure at a specific gravity of 0. The sugar in your homebrew will increase the density of the liquid and thus increase your reading.
The most important readings are taken right before fermentation and right before bottling. You want to make sure the proper sugar level is present during each of these steps as a confirmation that you are ready to proceed to the next step.