  Spin current and spin torque generation through the spin-orbit interactions
in solids, of bulk or interfacial origin, is at the heart of spintronics
research. The realization of spin-orbit torque (SOT) driven magnetic dynamics
and switching in diverse magnetic heterostructures also pave the way for
developing SOT magnetoresistive random access memory and other novel SOT memory
and logic devices. Of scientific and technological importance are accurate and
efficient SOT quantification techniques, which have been abundantly developed
in the last decade. In this article, we summarize popular techniques to
experimentally quantify SOTs in magnetic heterostructures at micro- and
nano-scale. For each technique, we give an overview of its principle,
variations, strengths, shortcomings, error sources, and any cautions in usage.
Finally, we discuss the remaining challenges in understanding and quantifying
the SOTs in heterostructures.
