How is the size of a religion determined for the purposes of this list?
When referring to the "size" of a religion, what is usually meant is its number of adherents. Other measurements, such as how many churches or meeting places a faith group owns or how many congregations/meeting groups there are, can also be instructive, but are usually not used as a measure of overall size. Measures of religiosity and the degree to which a religious tradition has a meaningful impact on its adherents may be more important than raw adherent counts, but such measures are not as readily available nor are they easily comparable between groups.