Instruments that measure moisture in ambient air; types include indicator papers and dial-styles; electronic versions may be analog or digital; may be traceable to NIST. Because humidity is affected by temperature, most hygrometers include thermometers to correct readings.

Hygrometers, or humidity meters, are devices for measuring the level of water vapor (also known as relative humidity, RH) in the atmosphere or in other gases.

How Are Hygrometers Used?
• Monitoring moisture levels in laboratory incubators, growth chambers, greenhouses, and controlled climate cabinets
• Measuring humidity in confined spaces, rooms, or buildings where moisture levels are critical to the activity being performed or to the objects or materials being stored
• Measuring humidity in domestic or residential settings
• Meteorological and climate monitoring

Classical, mechanical hygrometers, which are less widely used today, include wet/dry bulb hygrometers or psychrometers and hair tension hygrometers, which rely upon a single (hygroscopic) hair or fiber.

Most hygrometers available on the market today are electronic digital instruments, which measure humidity using capacitive or resistive sensors. These digital devices offer clear displays with reliable and consistent performance, and are typically compact, hand-held, or benchtop units with a minimal footprint. They may also be available with temperature, timer and alarm functionality, and with externally corded probes and wireless radio-signal connectivity for remote monitoring and data logging. Many operate over a wide temperature range of -5° to +50°C, with a typical measurement range of 0 to 95% relative humidity (RH).