The calculated distance (air line) between Merthyr Tydfil and Tonyrefail is approximately 12 miles respectively 19 kilometers.
By car or train, the actual journey to Tonyrefail is certainly longer, as only the direct route (as the crow flies) between Merthyr Tydfil and Tonyrefail has been calculated here.
Air line (approximately)
19 kilometers
10 nautical miles