Which measurement unit is primarily used to express impedance?

Impedance is an important concept in electrical engineering and is primarily expressed in ohms. This unit quantifies the opposition that a circuit or component presents to the flow of alternating current (AC). Impedance not only accounts for resistance but also incorporates the effects of inductance and capacitance, making it a more comprehensive measurement in AC circuits compared to DC circuits.

In contrast, volts measure electric potential, amperes measure electric current, and watts quantify power. While these units play significant roles in electrical calculations and relationships, they do not specifically relate to the concept of impedance in the same manner that ohms do. Thus, ohms is the correct choice for expressing impedance.