The calculated distance (air line) between Thái Nguyên and Đống Đa is approximately 40 miles respectively 65 kilometers.
By car or train, the actual journey to Đống Đa is certainly longer, as only the direct route (as the crow flies) between Thái Nguyên and Đống Đa has been calculated here.
Air line (approximately)
65 kilometers
35 nautical miles