What do most humidity sensors measure?

• A. Dew point.
• B. Percent relative humidity.
• C. Absolute humidity.
• D. Temperature.

Answer: (B)

Most humidity sensors measure relative humidity. Relative humidity is the percentage of water vapor in the air relative to the maximum amount the air can hold at the current temperature. This is the practical, widely used metric because it directly relates to how humidity affects comfort, condensation risk, and material behavior, and it aligns with how the common sensing technologies work (capacitive or resistive sensors whose output changes as moisture in the air changes). Dew point can be derived from relative humidity and temperature, but it’s not what the sensor typically outputs directly. Absolute humidity—water mass per volume—and temperature are different quantities; temperature is a separate measurement that the system may use to interpret RH.