The calculated distance (air line) between Mainz and Gau-Algesheim is approximately 12 miles respectively 19 kilometers.
By car or train, the actual journey to Gau-Algesheim is certainly longer, as only the direct route (as the crow flies) between Mainz and Gau-Algesheim has been calculated here.
Air line (approximately)
19 kilometers
10 nautical miles