| Harrow to Opole | 793.13 mi (1,276.42 km) |
| Harrow to Orzesze | 836.17 mi (1,345.68 km) |
| Harrow to Osowa | 803.97 mi (1,293.86 km) |
| Harrow to Ostroda | 861.02 mi (1,385.68 km) |
| Harrow to Ostroleka | 927.33 mi (1,492.39 km) |
| Harrow to Ostrow Mazowiecka | 942.20 mi (1,516.32 km) |
| Harrow to Ostrow Wielkopolski | 777.21 mi (1,250.81 km) |
| Harrow to Ostrowiec Swietokrzyski | 937.90 mi (1,509.40 km) |
| Harrow to Ostrzeszow | 784.27 mi (1,262.16 km) |
| Harrow to Oswiecim | 858.33 mi (1,381.35 km) |
| Harrow to Otwock | 919.78 mi (1,480.24 km) |
| Harrow to Ozarow Mazowiecki | 899.39 mi (1,447.43 km) |
| Harrow to Ozimek | 805.04 mi (1,295.59 km) |
| Harrow to Ozorkow | 837.07 mi (1,347.13 km) |
| Harrow to Pabianice | 843.86 mi (1,358.07 km) |
