How to Test a Hygrometer

Table salt can help you test your hygrometer.
Table salt can help you test your hygrometer. (Image: Salt Shaker by Window image by kellykramer from

Hygrometers are tools that measure relative humidity in different environments. Knowing the level of humidity is helpful when working with concrete and can be eye opening to have an understanding of the humidity level of your home. Certain fungus and molds multiply when humidity levels are above 50 to 55 percent, which can have an impact on health-related issues. Therefore, making sure your hygrometer is reading humidity levels accurately is important. There are two ways to test the hygrometer.

Things You'll Need

  • Cloth
  • Ziploc baggy
  • Bottle lid, small
  • Table salt
  • Water
  • Hygrometer

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Place the hygrometer on top of a damp washcloth. Use only water. Do not use soap or any other liquid, as this could damage the hygrometer.

Leave the hygrometer there for 6 to 8 hours undisturbed.

Read the hygrometer indicator. It should read at around 95 percent. If it doesn’t, then follow the manufacturer’s instructions to manually set the reading at 95 percent.


Place some table salt inside a small plastic bottle lid. You could also use a lid from a jam or other bottle lid if need be.

Wet the table salt enough to be mushy and damp, but not runny.

Place the lid with the mushy table salt inside a sealable plastic baggy with the hygrometer next to it inside the bag. Make sure the hygrometer is not touching the salt to avoid damage to the hygrometer. Seal the baggy with some air in it, and let it sit for 6 to 8 hours.

Observe the reading on the hygrometer. It should read somewhere close to 75 percent. If it doesn’t, then follow the manufacturer’s instructions to manually set the hygrometer to that setting.

Tips & Warnings

  • The difference between the two readings for the two tests is that the washcloth test has the hygrometer sensing units sitting directly on a concentrated moisture. The salt in the bottle cap test has the hygrometer's sensing units placed near the source of the moisture, not on it.
  • Do not disturb the hygrometers during the test. It can take 2 to 3 hours for results to begin appearing in the display window. Keep the testing environment at a constant temperature if at all possible, as differences in heat in the room will make a difference in the moisture readings. If your hygrometer displays zero readings, make sure the device is turned on, and repeat the tests. If you still do not get any readings, then the hygrometer is broken, and you will need to have it repaired or replaced.


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