How to Calibrate a Hygrometer

You may be wondering, "I have a digital hygrometer. Do I even need to calibrate it?" The answer is yes. Calibrating a hygrometer is essential to ensuring the accuracy of humidity readings and maintaining optimal environments. No matter what type of hygrometer you may use, digital or analog, calibrating is key to ensuring accurate measurements when seasoning a humidor or monitoring your humidity. It is not a difficult task but there are a few different approaches. We've drawn up a couple of ways to go about calibrating your hygrometer so that you can choose the one that fits your needs best.

With the advancement of different humidification products, it has become easier than ever to keep your humidor properly humidified. And as with many other Boveda products, their calibration kit is simple and straight forward. Take your hygrometer and place it in the provided bag. Leave it there for 24 hours, and if it reads 75% RH after the time is up, it is properly calibrated.

The Salt Test:

Luckily, as nature would have it, when salt and water (NaCl and H2O for you studious types), are in a saturated solution at equilibrium, the resultant humidity is 75%. This gives a fantastic reference point to calibrate our hygrometer. Here's the procedure you should use: you need a Ziploc bag, a screw-on beer bottle cap (or another small container) a small amount of salt (regular 'ole table salt), and water.

1. Place the salt in the bottle cap (or another small container).
2. Dampen the salt with water. Do not put so much in that the salt gets "sloppy". You want a damp pile of salt in the bottle cap.
3. Place both the hygrometer and the bottle cap full of damp salt in the Ziploc bag and seal it well. (It is important not to let air on or out while the test is going on.)
4. Keep it like this for over 8 hours.

After 8 hours in the damp salt environment, the actual humidity inside the bag will be 75%. Compare this to your hygrometer which should also read 75% RH.

The Towel Test:

Dampen a towel (not dripping wet, but good and damp), then wrap the hygrometer in the towel for 30 to 45 minutes. Then unwrap it and read the humidity (quickly). If your hygrometer is perfectly calibrated (few are) it will be reading exactly 100% humidity. Most likely, it will be reading somewhere between 80 and 90%.

How to Adjust Your Hygrometer

No matter which method you choose, you may be wondering what to do once you get the reading. If your hygrometer is not calibrated properly, you have a few options. If you have a hygrometer that can be adjusted, tweak the reading to the proper level and you are calibrated. If you are unable to adjust the calibration, make note of how far off your hygrometer is so that you can add or subtract that amount when reading the hygrometer.

Learn more about humidors and maintenance in our humidors section of Cigar 101, here at CI!