| Merthyr Tudful to Joliet (Illinois) | 3,852.19 mi (6,199.51 km) |
| Merthyr Tudful to Jonesboro (Arkansas) | 4,221.93 mi (6,794.54 km) |
| Merthyr Tudful to Joplin (Missouri) | 4,309.58 mi (6,935.59 km) |
| Merthyr Tudful to Joppatowne (Maryland) | 3,475.88 mi (5,593.89 km) |
| Merthyr Tudful to Juana Díaz (Puerto Rico) | 4,102.24 mi (6,601.91 km) |
| Merthyr Tudful to Junction City (Kansas) | 4,302.35 mi (6,923.96 km) |
| Merthyr Tudful to Juneau (Alaska) | 4,337.05 mi (6,979.81 km) |
| Merthyr Tudful to Jupiter (Florida) | 4,226.50 mi (6,801.90 km) |
| Merthyr Tudful to Jupiter Farms (Florida) | 4,230.89 mi (6,808.96 km) |
| Merthyr Tudful to Jurupa Valley (California) | 5,301.42 mi (8,531.81 km) |
| Merthyr Tudful to Justice (Illinois) | 3,829.43 mi (6,162.87 km) |
| Merthyr Tudful to Kahului (Hawaii) | 7,162.04 mi (11,526.18 km) |
| Merthyr Tudful to Kailua (Hawaii) | 7,150.78 mi (11,508.08 km) |
| Merthyr Tudful to Kalamazoo (Michigan) | 3,718.62 mi (5,984.54 km) |
| Merthyr Tudful to Kalispell (Montana) | 4,423.60 mi (7,119.10 km) |
