What unit is used for measuring fluid in the metric system?

In the metric system, the liter is the primary unit used for measuring fluid volume. The liter is specifically designed to quantify liquids, making it the standard measure in many scientific and medical contexts when dealing with fluids. For instance, in nursing and healthcare, dosages of medications, fluid intake and output, and various laboratory measurements are often expressed in liters or milliliters, which are subdivisions of the liter.

The other options, while part of the metric system, serve different purposes. Millimeters are a unit of length, grams are a unit of mass, and meters also measure length. Thus, they are not suitable for measuring liquid volumes. This distinction emphasizes the liter's crucial role in accurately and effectively communicating fluid measurements in various fields, including nursing.