Calibrate Your Hygrometer - Two Methods

Discussion in 'Incubating & Hatching Eggs' started by Intheswamp, Jan 14, 2010.

  1. Intheswamp

    Intheswamp Chillin' With My Peeps

    Mar 25, 2009
    South Alabama
    Calibrating a hygrometer is rather simple, but the question gets asked pretty often. Websites with a focus on cigars tend to be good sources of information regarding hygrometers and calibrating hygrometers. Below is a cut-n-paste from . It gives the basic information that is found many places, but it also gives a little more detail, shows another method other than the "salt method", and tells a little bit about how it works. It's a good short article to read, especially if you want to check your hygrometer's calibration. The second method I had never heard of...


    Submitted by Rob on June 22, 2008 – 11:56 pm

    The following methods will describe the “Salt” calibration method; you only need to perform the high test to have a fairly close reading. I am a perfectionist – so I will provide you with an optional second step for the most accurate calibration.

    Salt Method Calibration (High Reading):

    Place Morton Canning salt (a few tablespoons worth) in a small mug, glass, or container and mix in some distilled water. Make sure you do not dissolve the salt. The desired result should be a “sludgy”, “gooey”, semi-solid mixture.

    Place this mixture inside a zip lock bag (I prefer sliding lock to ensure complete closure) with your hygrometer inside. Make sure the hygrometer is facing up (so you can read it) and that no water or mixture comes in contact with the meter (this will throw off readings). Now seal this zip lock bag with an even larger bag to ensure that no additional air may enter in.

    The proper stabilization time of this mixture will take approximately 12 hours. At this point your hygrometer should read in the 75% range. I would perform this test various times to get the average, and use this as the tuning number. (Ex: 70% = 5 points, 74% = 1 point, 72% = 3 points. 9/3=3. Adjust by 3 percent.) If your hygrometer allows tuning it is usually done by turning the screw on the back with a small screwdriver.

    You are now ready to use it to measure your humidity! – Unless you want to know how exact it really is…

    The Low Calibration:

    We are going to follow the exact same steps as above, however this time we are going to use something called Magnesium Chloride Flakes (eBay this). The flakes are inexpensive and when mixed with distilled water (the same “sludge”) it creates a constant humidity of 33%.

    Calibration of your hygrometer should happen twice a year.

    Why Does This Work: The mixture of Salt and distilled water and Magnesium Chloride and distilled water has a fixed vapor. The vapor will create a constant humidity regardless of the amount of mixture if the mixture still remains a solid. Temperature plays the minutest role in the amount of humidity created; over a 25 degree window of 60-85 degrees (F) the change is .xx % in the reading of 75.xx %.​
  2. Karrie13

    Karrie13 Chillin' With My Peeps

    May 1, 2009
    Wow! Thanks for the information.
  3. kyrose

    kyrose Chillin' With My Peeps

    Jul 29, 2009
    i have 2 new hygrometers and i tried this method.1 is reading 52 and the other it possible for them to be that off?
  4. SunnyChic

    SunnyChic Keep The Sunny Side Up

    Mar 7, 2009
    Thanks for posting this! [​IMG]
  5. flgardengirl

    flgardengirl Chillin' With My Peeps

    Dec 2, 2009
    Sunny side up :)
    I am recalibrating mine again now before my second hatch because it was 19 off for the first hatch and now it is reading correctly.. the same as our house hygrometer which is correct. So I wonder if they calibrate themselves over time? It was fairly new (a few days old) the first hatch but had been sitting inside the house but it was way off when I calibrated it. So I will do it again tonight before I lock down tomorrow morning to make sure.. Kinda wierd.
    Last edited: Jan 14, 2010
  6. kryptoniteqhs

    kryptoniteqhs Rosecomb Rich

    Nov 14, 2008
    Perris, CA
    Quote:yes...i am wondering the same thing....i have one showing 55 & one showing 65
  7. Serrin

    Serrin Chillin' With My Peeps

    Thanks for the C&P of this great information. I have heard of the salt method, but never the Magnesium Chloride Flakes way for the low end. That should make for a pretty accurate Hygrometer IMHO! [​IMG] Thanks for sharing!
  8. Intheswamp

    Intheswamp Chillin' With My Peeps

    Mar 25, 2009
    South Alabama
    Glad to help. [​IMG]


    BTW, I can resemble the part about your log cabin in your signature line.
  9. Intheswamp

    Intheswamp Chillin' With My Peeps

    Mar 25, 2009
    South Alabama
    Some folks have been asking about calibrating their hygrometere and I thought I'd bump this up a bit so it would be in the "search" range. Sorry for the noise. [​IMG]

  10. Gentry1350

    Gentry1350 Chillin' With My Peeps

    Great information! I'm thinking my digital hygrometers are 11 and 14% off. Yikes! I'm getting somewhat expensive eggs tomorrow. No wonder my hatch rates have been so low!

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