This calculator predicts the final gravity given the original gravity and yeast strain used. Apparent attenuation refers to this apparent reduction in gravity between the start of fermentation and completion. Different yeasts have different characteristic degrees of attenuation. These are often given as a range of percentages.

The left hand side of the calculator contains the main inputs and outputs. There is a box to type your beer's original gravity and a drop-down menu to select your yeast strain. Lower on the left is the output values apparent attenuation and predicted final gravity.

The box on the right contains a number of "Filter Options". You can choose from these criteria to help you narrow down the yeast strains available. Changing the filter options automatically adjusts the options provided under "Yeast Strain" to only those strains that match the set criteria. You can set any combination of these criteria simultaneously, but there might not be a yeast strain to match some combinations.

The Ale / Lager filter option allows you to limit the visible yeast to only ale strains or only lager strains.

The Beer Style option allows you to select from many of the BJCP styles and limit the strains to ones considered compatible with each style.

Fix-class selects for yeasts based loosely on the classification scheme proposed by Fix [3] and mentioned in White and Zainasheff [4]. Clean ale yeasts (i.e. neutral flavors) produce minimal fermentation character with low concentrations of yeast byproducts. Fruity ale yeasts produce more noticeable fruity-esters and enhance the perception of malt sweetness. Phenolic ale yeasts have the genetics needed to produce phenols – chemical compounds that may taste like bananas, medicine, smoke, or other things. Dry lager strains produce a crisp effect that emphasizes hop bitterness. Full lager strains produce beers with more mouthfeel that emphasize maltiness. Wild is a catchall for less common microorganisms including several types of brettanomyces and bacteria sometimes used in brewing.

Region of Origin allows you to limit your search to yeasts associated with certain countries and regions.

Flocculation refers to the tendency of yeast cells to stick together. This affects how long the cells remain in solution and in turn affects degree of attenuation. More time floating around means more time to eat available sugars. Low flocculation causes distinctively cloudy beer due to the yeast remaining suspended in the beer. Low flocculating yeasts often produce phenols and have high attenuation. Medium flocculation tends to be associated with clean flavors and also have fairly high attenuation. Many lager strains and lager-like ale strains have medium flocculation. Highly flocculating yeast tends to attenuate less because they drop out of solution earlier. Many ester producing English strains have notably high flocculation.

Yeast Form refers to whether the strain comes as a packet of dry yeast granules or as liquid yeast slurry.

Alc. Tolerance refers to the concentration of alcohol a strain can tolerate and continue to be active. Strains with low alcohol tolerance will not be able to ferment as much of the sugars in high gravity wort before becoming dormant.

Manufacturer allows you to narrow your options to only yeasts produced by a particular company.