--- title: What is “Relative Humidity” and How Is It Measured in Q-FOG Testers? description: Humidity is a general term that describes the amount of water vapor in the air. Humidity is a critical element of the outdoor environment and contributes to the material degradation in both weathering and corrosion. image: https://blog.q-lab.com/hubfs/Realative_Humidity_Q-FOG_how_its_measured.jpg --- [![q-lab-loog-standlards-landing](https://blog.q-lab.com/hs-fs/hubfs/Logos%20and%20Assets/q-lab-loog-standlards-landing.png?width=150&name=q-lab-loog-standlards-landing.png "q-lab-loog-standlards-landing")](https://blog.q-lab.com/) - [Q-Lab.com](https://www.q-lab.com) - [Testing Services](https://q-lab.com/test-services/) - [Products](https://q-lab.com/products/) # Q-Lab Weathering & Corrosion Blog Read the latest news and articles from the experts. #### Filter Posts by Category - [Weathering](https://blog.q-lab.com/tag/weathering) - [Corrosion](https://blog.q-lab.com/tag/corrosion) - [FAQ](https://blog.q-lab.com/tag/faq) - [Outdoor](https://blog.q-lab.com/tag/outdoor) - [Case Study](https://blog.q-lab.com/tag/case-study) # What is “Relative Humidity” and How Is It Measured in Q-FOG Testers? Posted by [Sean Fowler](https://blog.q-lab.com/author/sean-fowler) on Jul 21, 2021 11:02:24 AM Humidity is a general term that describes the amount of water vapor in the air. Humidity is a critical element of the outdoor environment and contributes to the material degradation in both weathering and corrosion. Humidity can be expressed as either an Absolute Humidity or a Relative Humidity (RH). Absolute humidity is the mass of water vapor in a given volume of air, expressed as g/m³. Relative Humidity (RH) represents the amount of water vapor in the air vs. how much it would contain if fully saturated, expressed as a percentage. Relative humidity is used much more commonly both in determining human comfort level and when describing natural and accelerated weathering. Relative humidity can be measured a number of ways. Q-Lab uses two methods in our testers - electronic measurement with a digital hygrometer is used in [Q-SUN](https://www.q-lab.com/products/q-sun-xenon-arc-test-chambers/q-sun-xe-3) xenon arc testers and mechanical measurement with a wet bulb/dry bulb hygrometer is used in [Q-FOG](https://www.q-lab.com/products/q-fog-cyclic-corrosion-chamber/q-fog-crh-cyclic-corrosion-tester) corrosion test chambers. Digital hygrometers are relatively common in everyday life. A digital hygrometer doesn’t require significant air flow, which makes it ideal for use in the Q-SUN tester and for ambient lab measurements. Digital hygrometers are readily available and simple to package. A wet/dry bulb hygrometer uses thermometers, which makes it relatively easy to calibrate compared to a digital hygrometer. The wet/dry bulb requires a lot of air flow, which isn’t a problem in the Q-FOG tester’s blower module, and is also easy to maintain free from corrosion. Salt fog would degrade and eventually destroy a digital hygrometer if it were used in a Q-FOG chamber. To read more about Q-Lab and to find more articles like this, please visit the [Q-Lab Blog](https://blog.q-lab.com/?hsLang=en). Topics: [Corrosion](https://blog.q-lab.com/topic/corrosion?hsLang=en), [Q-FOG](https://blog.q-lab.com/topic/q-fog?hsLang=en) - [Tweet](https://twitter.com/share) **Q-Lab Corporation is a global provider of material durability testing products. We design and manufacture Q-PANEL standard test substrates as well as weathering, light stability, and corrosion testers. Q-Lab also offers A2LA accredited contract test services, including accelerated laboratory testing. Our weathering products and services are used by materials scientists, research and development engineering, and quality control personnel in numerous industries.** [Read More](https://q-lab.com/about/) - [Q-Lab.com](https://www.q-lab.com) - [QUV Accelerated Weathering Test Chambers](https://q-lab.com/products/quv-weathering-tester/quv) - [Q-SUN Xenon Test Chambers](https://q-lab.com/products/q-sun-xenon-arc-test-chambers) - [Q-FOG Corrosion test Chambers](https://q-lab.com/products/q-fog-cyclic-corrosion-chamber) - [Testing Services](https://q-lab.com/test-services/) Subscribe To Notification Updates ### Subscribe to update notifications © 2026 Q-Lab Corporation ![Tagline_CMYKBlue_Logo_Left](https://blog.q-lab.com/hs-fs/hubfs/Logos%20and%20Assets/Tagline_CMYKBlue_Logo_Left.png?width=300&name=Tagline_CMYKBlue_Logo_Left.png "Tagline_CMYKBlue_Logo_Left")