The calculated distance (air line) between Dayr Ḩāfir and Manbij is approximately 29 miles respectively 47 kilometers.
By car or train, the actual journey to Manbij is certainly longer, as only the direct route (as the crow flies) between Dayr Ḩāfir and Manbij has been calculated here.
Air line (approximately)
47 kilometers
25 nautical miles