The calculated distance (air line) between Al Qaţīf and Al Muharraq is approximately 43 miles respectively 69 kilometers.
By car or train, the actual journey to Al Muharraq is certainly longer, as only the direct route (as the crow flies) between Al Qaţīf and Al Muharraq has been calculated here.
Air line (approximately)
69 kilometers
37 nautical miles