* Convert to the same unit: Let's convert decimeters to millimeters. There are 100 millimeters in 1 decimeter. So, 1.9 decimeters is equal to 1.9 * 100 = 190 millimeters.

* Compare: Now we have:

* 190 millimeters

* 1900 millimeters

* Conclusion: 1900 millimeters is bigger than 190 millimeters.

Therefore, 1900 millimeters is bigger than 1.9 decimeters.