If the ruler you use is marked with millimeters and centimeters, you can say you use metrical measurements.
The adjective metrical is a less common way to say metric, as in the metric system of measurement. Instead of using inches and feet, a metrical system uses centimeters and meters as units for measuring length. Most countries measure metrical distances, size, and lengths, although the United States doesn't. The root of metrical is the Greek word metron, which means "measure."