A church can be measured by various criteria in order to determine its size. Such measures include area, volume, length, width, height, or capacity. Several churches individually claim to be "the largest church", which may be due to any one of these criteria. St. Peter's Basilica in Vatican City, the largest church in the world. This list includes extant churches that have a known area of more than 2,000 square metres (22,000 sq ft). Entries are included even if they currently do not function as a church. For example, the Hagia Sophia is included – it was originally built as a church but was later converted into a mosque. Churches are not included if no reliable sources are available for their stated sizes.