| Watford to Smolyan | 1,369.18 mi (2,203.49 km) |
| Watford to Sofia | 1,266.29 mi (2,037.90 km) |
| Watford to Sopot | 1,325.94 mi (2,133.89 km) |
| Watford to Sozopol | 1,456.72 mi (2,344.36 km) |
| Watford to Sredets | 1,438.74 mi (2,315.43 km) |
| Watford to Stamboliyski | 1,338.80 mi (2,154.58 km) |
| Watford to Stara Zagora | 1,371.63 mi (2,207.42 km) |
| Watford to Svilengrad | 1,421.94 mi (2,288.40 km) |
| Watford to Svishtov | 1,311.93 mi (2,111.34 km) |
| Watford to Targovishte | 1,377.34 mi (2,216.62 km) |
| Watford to Teteven | 1,295.27 mi (2,084.54 km) |
| Watford to Troyan | 1,315.01 mi (2,116.30 km) |
| Watford to Tryavna | 1,347.78 mi (2,169.04 km) |
| Watford to Tutrakan | 1,348.28 mi (2,169.85 km) |
| Watford to Varna | 1,434.20 mi (2,308.13 km) |
