| Montmartin-sur-Mer | |
|---|---|
|   The church | |
| Coordinates: 48°59′22″N1°31′24″W / 48.9894°N 1.5233°W | |
| Country | France | 
| Region | Normandy | 
| Department | Manche | 
| Arrondissement | Coutances | 
| Canton | Quettreville-sur-Sienne | 
| Intercommunality | Coutances Mer et Bocage | 
| Government | |
| • Mayor (2020–2026) | Bruno Quesnel [1] | 
| Area 1 | 9.81 km2 (3.79 sq mi) | 
| Population  (2022) [2]  | 1,413 | 
| • Density | 140/km2 (370/sq mi) | 
| Time zone | UTC+01:00 (CET) | 
| • Summer (DST) | UTC+02:00 (CEST) | 
| INSEE/Postal code |  50349 /50590 | 
| Elevation | 2–60 m (6.6–196.9 ft) (avg. 50 m or 160 ft) | 
| 1 French Land Register data, which excludes lakes, ponds, glaciers > 1 km2 (0.386 sq mi or 247 acres) and river estuaries. | |
Montmartin-sur-Mer is a commune in the Manche department in Normandy in north-western France.