How to Calibrate a Hygrometer

A hygrometer is a simple device that is used to measure relative humidity, which is the ratio of actual moisture in the air compared to the total amount of moisture the air can hold at a given temperature.
As simple as hygrometers may be, however, they can be quite delicate and prone to giving inaccurate readings over time or with use. Using nothing more than a few kitchen supplies, you can determine the accuracy of your hygrometer and calibrate it accordingly.

Step 1

Mix the salt and water in a small cup, stirring until totally saturated. After a few minutes, the mixture should resemble wet sand.

Step 2

Place the cup and hygrometer in a resealable plastic bag. Keep the salt and the hygrometer completely separate.

Step 3

Seal the bag and place it aside to sit at a consistent room temperature, away from drafts or direct sunlight. Let sit for 8 to12 hours.

Step 4

Check the hygrometer, while keeping the bag completely sealed. In ideal conditions, the humidity should read as 75 percent. (Your hygrometer may be off by a couple of points.)

Step 5

Remove the hygrometer from the bag. If you can, quickly adjust it to read 75 percent; otherwise, simply make a note as to how much you need to adjust your figure for each reading.

Things You Will Need

  • 1/2 cup of table salt
  • 1/4 cup of water
  • Hygrometer
  • Resealable plastic bag

Tip

  • Before taking a reading, always try to give your hygrometer two hours to stabilize, so that it can register subtle changes accurately. You can use your hygrometer to be sure that the humidity in your home is low enough to discourage the growth of mold or to facilitate the storage of humidity-sensitive items such as cigars.

Warning

  • Handle your hygrometer gently, to avoid damaging its delicate parts.