The calculated distance (air line) between Stansted Mountfitchet and Swansea is approximately 178 miles respectively 287 kilometers.
By car or train, the actual journey to Swansea is certainly longer, as only the direct route (as the crow flies) between Stansted Mountfitchet and Swansea has been calculated here.
Air line (approximately)
287 kilometers
155 nautical miles