A list of the world's longest churches can be found in the floor of the nave in San Pietro in Vaticano. The purpose of the inscriptions is to illustrate the size of the basilica, making it absolutely clear that it is the largest of them all.
The inscriptions are in Latin, but here is a list with the English names of the churches, starting with St Peter's:
- St Peter's in the Vatican: 186.30 m
- St Paul's, London, UK: 158.10 m
- The Duomo, Florence, Italy: 149.28 m
- Sacred Heart of Jesus, Brussels, Belgium: 140.94 m
- Immaculate Conception, Washington DC, USA: 139.14 m
- Rheims Cathedral, Rheims, France: 138.69 m
- The Duomo, Milan, Italy: 134.94 m
- Cologne Cathedral, Cologne, Germany: 134.94 m
- Speyer Cathedral, Speyer, Germany: 134 m
- San Petronio, Bologna, Italy: 132.54 m
- Seville Cathedral, Sevilla, Spain: 132 m
- St Paul's Outside the Walls, Rome, Italy: 131.66 m
- Notre Dame, Paris, France: 130 m
- St Vitus, Prague, Czech Republic: 124 m
- Toledo Cathedral, Toledo, Spain: 122 m
- St John Lateran, Rome, Italy: 121.84 m
- La Plata Caethedral, La Plata, Argentina: 120 m
- Mexico City Cathedral, Mexico City, Mexico: 119.55 m
- Antwerp Cathedral, Antwerp, Belgium: 118.60 m
- Santa Giustina, Padua, Italy: 118.50 m
- Esztergom Cathedral, Esztergom, Hungary: 118 m
- Ferrara Cathedral, Ferrara, Italy: 118 m
- Basilica of Santa Maria degli Angeli, Assisi, Italy: 114.76 m
- St Mary's Cathedral, Sydney: 114.61
- St Paul's, Brasilia, Brazil: 111.45 m
- Westminster Cathedral[1], London: 110 m
- Hagia Sophia[2], Istanbul, Turkey: 109.57 m
- Cathedral of the Holy Cross, Boston, USA: 103.50 m
- Basilica of the Virgin Mary, Gdansk, Poland: 103.50 m
- Cathedral of Our Lady of the Angels, Los Angeles, USA: 101.25 m
- St Patrick's, New York, USA: 101.19 m