Pick up a hydrometer from my shop! http://www.biyhomebrewsupply.com/collections/equipment/products/allahydrometer
A hydrometer is a very useful tool used by brewers of all types that provides readings that allow the user to calculate the final alcohol content of a particular brew. A hydrometer allows the reader to essentially view the density of a liquid as a numerical value. By running a starting reading and a final reading through a simple equation, the brewer will have a very accurate approximation of what the alcohol content is. Different hydrometers take different readings, but most feature both gravity readings as well as Brix readings. More advanced hydrometers even offer potential alcohol assumptions. A hydrometer is used by simply dropping it into a sample of the wort. The weighted end of the hydrometer then pulls it into the sample until it steadies out and a reading can be obtained by looking at where the fluid touches the hydrometer.