| Harpenden to Opole | 792.81 mi (1,275.91 km) |
| Harpenden to Orzesze | 836.38 mi (1,346.02 km) |
| Harpenden to Osowa | 798.42 mi (1,284.94 km) |
| Harpenden to Ostroda | 856.48 mi (1,378.36 km) |
| Harpenden to Ostroleka | 923.54 mi (1,486.29 km) |
| Harpenden to Ostrow Mazowiecka | 938.70 mi (1,510.70 km) |
| Harpenden to Ostrow Wielkopolski | 775.53 mi (1,248.10 km) |
| Harpenden to Ostrowiec Swietokrzyski | 936.65 mi (1,507.39 km) |
| Harpenden to Ostrzeszow | 782.90 mi (1,259.96 km) |
| Harpenden to Oswiecim | 858.58 mi (1,381.75 km) |
| Harpenden to Otwock | 917.14 mi (1,475.99 km) |
| Harpenden to Ozarow Mazowiecki | 896.67 mi (1,443.04 km) |
| Harpenden to Ozimek | 804.66 mi (1,294.98 km) |
| Harpenden to Ozorkow | 834.79 mi (1,343.47 km) |
| Harpenden to Pabianice | 842.00 mi (1,355.06 km) |
