| Watford to Orbetello | 837.07 mi (1,347.13 km) |
| Watford to Oria | 1,152.18 mi (1,854.25 km) |
| Watford to Oristano | 918.48 mi (1,478.15 km) |
| Watford to Orta Nova | 1,042.56 mi (1,677.84 km) |
| Watford to Orte | 872.52 mi (1,404.19 km) |
| Watford to Ortona | 945.08 mi (1,520.95 km) |
| Watford to Orvieto | 849.84 mi (1,367.69 km) |
| Watford to Orzinuovi | 639.33 mi (1,028.91 km) |
| Watford to Osimo | 856.16 mi (1,377.86 km) |
| Watford to Ospitaletto | 636.38 mi (1,024.16 km) |
| Watford to Ostuni | 1,138.48 mi (1,832.21 km) |
| Watford to Ottaviano | 1,026.84 mi (1,652.53 km) |
| Watford to Ovada | 638.36 mi (1,027.35 km) |
| Watford to Ozieri | 885.85 mi (1,425.64 km) |
| Watford to Paceco | 1,134.21 mi (1,825.33 km) |
