An inclinometer or clinometer is an instrument used for measuring angles of slope, elevation, or depression of an object with respect to gravity’s direction. Clinometers measure both inclines and declines using three different units of measure: degrees, percentage points, and topo. A tilt sensor can measure the tilting in often two axes of a reference plane in two axes.

Hand-held clinometers are used for a variety of surveying and measurement tasks. In land surveying and mapping, a clinometer can provide a rapid measurement of the slope of a geographic feature, or used for cave survey. In prospecting for minerals, clinometers are used to measure the strike and dip of geologic formations. In forestry, tree height measurement can be done with a clinometer using standardized methods including triangulation. Major artillery guns may have an associated clinometer used to facilitate aiming of shells over long distances. Permanently-installed tiltmeters are emplaced at major earthworks such as dams to monitor the long-term stability of the structure.