The calculated distance (air line) between Merthyr Tydfil and Brynmawr is approximately 9 miles respectively 15 kilometers.
By car or train, the actual journey to Brynmawr is certainly longer, as only the direct route (as the crow flies) between Merthyr Tydfil and Brynmawr has been calculated here.
Air line (approximately)
15 kilometers
8 nautical miles