| Southborough to Popovo | 1,322.92 mi (2,129.03 km) |
| Southborough to Provadia | 1,379.79 mi (2,220.56 km) |
| Southborough to Radnevo | 1,351.44 mi (2,174.93 km) |
| Southborough to Radomir | 1,218.67 mi (1,961.26 km) |
| Southborough to Rakitovo | 1,288.49 mi (2,073.63 km) |
| Southborough to Rakovski | 1,311.92 mi (2,111.33 km) |
| Southborough to Razgrad | 1,327.99 mi (2,137.19 km) |
| Southborough to Razlog | 1,267.75 mi (2,040.25 km) |
| Southborough to Ruse | 1,293.51 mi (2,081.71 km) |
| Southborough to Samokov | 1,252.17 mi (2,015.17 km) |
| Southborough to Sandanski | 1,273.96 mi (2,050.24 km) |
| Southborough to Sevlievo | 1,288.51 mi (2,073.66 km) |
| Southborough to Shumen | 1,354.92 mi (2,180.53 km) |
| Southborough to Silistra | 1,338.32 mi (2,153.81 km) |
| Southborough to Sliven | 1,352.81 mi (2,177.14 km) |
