How to Measure Humidity in a Room

High humidity can cause condensation to form indoors.

The level of moisture in air is known as humidity. It varies according to outside temperature and climate. For example, summer in subtropical regions such as Louisiana usually creates high humidity levels. In dry regions such as Utah, humidity levels may be much lower. Extremes of humidity can cause health problems, particularly bronchial and breathing issues. It's possible to measure the humidity level in a room using a common mechanical device known as a hygrometer.

Things You'll Need

• Mechanical hygrometer
• Small cup
• Half cup of salt
• Water
• Box with tight lid

Instructions

1. Visit a hardware store and purchase a hygrometer. These devices are available in digital or analog form. The latter is usually cheaper to buy than digital versions and in some cases more accurate over a wider range of readings. The following steps cover analog hygrometer usage.

2. Ensure that the hygrometer is calibrated. The store clerk may confirm this for you. Some stores may also sell one-step calibration packs. However, it's straightforward and free to calibrate at home.

   Fill a small cup halfway up with salt. Add approximately 1/4 cup of water to the salt. The salt should be damp, but not too wet. Put the cup in the bottom of a large plastic box. Place the hygrometer in the same box, making sure the hygrometer doesn't touch the salt. Seal the box and leave it for at least six hours.

3. Open the sealed box and remove the hygrometer. The dial should read 75 percent. This is the humidity level created by damp salt in a sealed environment. If it doesn't read this figure, adjust the device by turning the calibration wheel until it's at 75 percent.

4. Set the hygrometer down in the room in which you want to measure the humidity. Leave the unit to settle for an hour or two.

5. Check the readings on the hygrometer. Healthy levels of humidity are considered to be between 30 to 50 percent, according to the Canada Mortgage and Housing Association.

Tips & Warnings

• Keep your hygrometer away from radiators and other heat sources in a room. These could skew the results.

References

• Canada Mortgage and Housing Association: Measuring Humidity in Your Home
• USA Today: How Humidity is Measured