| Merthyr Tudful to Mauldin (South Carolina) | 3,933.61 mi (6,330.54 km) |
| Merthyr Tudful to Maumee (Ohio) | 3,674.90 mi (5,914.19 km) |
| Merthyr Tudful to Maumelle (Arkansas) | 4,337.68 mi (6,980.82 km) |
| Merthyr Tudful to Mayagüez (Puerto Rico) | 4,121.26 mi (6,632.53 km) |
| Merthyr Tudful to Mayfield Heights (Ohio) | 3,589.69 mi (5,777.05 km) |
| Merthyr Tudful to Mays Chapel (Maryland) | 3,487.48 mi (5,612.55 km) |
| Merthyr Tudful to Maywood (California) | 5,325.89 mi (8,571.19 km) |
| Merthyr Tudful to Maywood (Illinois) | 3,823.84 mi (6,153.87 km) |
| Merthyr Tudful to McAlester (Oklahoma) | 4,466.02 mi (7,187.37 km) |
| Merthyr Tudful to McAllen (Texas) | 5,012.79 mi (8,067.31 km) |
| Merthyr Tudful to McCalla (Alabama) | 4,198.61 mi (6,757.00 km) |
| Merthyr Tudful to McComb (Mississippi) | 4,440.60 mi (7,146.46 km) |
| Merthyr Tudful to McDonough (Georgia) | 4,074.05 mi (6,556.56 km) |
| Merthyr Tudful to McFarland (California) | 5,264.77 mi (8,472.83 km) |
| Merthyr Tudful to McHenry (Illinois) | 3,820.11 mi (6,147.88 km) |
