| Călmățui | |
| Pushpin Map: | Romania |
| Subdivision Type1: | Country |
| Subdivision Name1: | Romania |
| Subdivision Type2: | Counties |
| Subdivision Name2: | Galați County |
| Subdivision Type3: | Villages |
| Subdivision Name3: | Grivița, Călmățui |
| Length: | 25km (16miles) |
| Mouth: | Siret |
| Mouth Coordinates: | 45.5528°N 27.6156°W |
| Basin Size: | 363km2 |
| Tributaries Right: | Herătău, Valea Ciorii |
The Călmățui is a left tributary of the river Siret in Romania. It discharges into the Siret near the village Tudor Vladimirescu. The basin size of the 25km (16miles) long Călmățui is 363km2.