Making sure your hygrometer is properly calibrated is fundamental if you want it to provide you with accurate readings. A plethora of tutorials and how-to guides on how to do this can be found on the internet.
However, our experience has taught us to take some of these with a pinch of salt.
In this dedicated guide, you will learn how to properly calibrate a hygrometer:
- Why Calibrate A Hygrometer?
- How To Accurately Calibrate A Hygrometer With Boveda
- Why You Shouldn’t Calibrate A Hygrometer With Salt
- How To Adjust A Hygrometer After Calibration
- How Often Should You Calibrate A Hygrometer?
Simply use the links above to jump ahead or scroll down to read it all!
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Why Do You Need To Calibrate A Hygrometer?
A hygrometer is an essential albeit sometimes overlooked component to any self-respecting humidor. Even with the best quality humidor, an accurate and calibrated hygrometer is fundamental.
As mentioned many times throughout our guides, hygrometers need to be properly calibrated to ensure that they provide you with accurate readings.
Cigars are natural products and they’re very sensitive to both humidity and temperature. Consequently, they need to be stored in a controlled environment to prevent them becoming dry or mouldy from too much moisture.
If you don’t have a device that allows you to monitor these levels, you’re essentially flying blind and won’t be able to properly care for your cigars.
The concept of calibrating a hygrometer is overall quite simple. You simply expose the hygrometer to a specific and verifiable relative humidity level for 24 hour. Afterwards, the hygrometer’s reading can be adjusted much like a watch.
Once you have a calibrated hygrometer, you will be confident about the readings in your humidor. Therefore, if you run into any anomalous readings, you know that it’s an issue with your storage and not the hygrometer that’s at fault.
How To Properly Calibrate A Hygrometer With Boveda
We’ve discussed using Boveda to calibrate a hygrometer in the brand’s dedicated guide. If you’ve just read that and were directed to come here, you’ll now learn how it works and why it’s our favourite method.
How To Use Boveda Calibration Kits [Best Method]
Of all the methods that we have tried, Boveda’s calibration kits are by far the easiest and most convenient. If you buy a Boveda Butler, they’re also supplied for free. However, they can be used with any hygrometer that can be calibrated.
Otherwise, a single calibration kit costs just under $8 on Amazon and it’s all that you will need for the process.
Once you have the calibration kit, simply proceed with the following steps:
- Open the calibration kit bag.
- Place the hygrometer inside.
- Leave for 24 hours.
- Adjust the hygrometer as described below.
Boveda also propose doing what they refer to as “two-point calibration”. This involves using the 75% calibration kit for 24 hours, making the necessary adjustment to the hygrometer, and then repeating the process with a 32% calibration kit.
Consequently, the hygrometer will be calibrated by taking into account by high and low levels. As a result, it will be more accurate across the full spectrum.
Bear in mind that once you have used the packs, they won’t be quite as accurate for future calibrations. While you can do more than one in a pinch, it might not be quite enough if accuracy if your objective.
How To Use Regular Boveda Packs To Calibrate [In Emergencies]
Boveda Butler In A Boveda Humidor Bag
Although we prefer the calibration kits, it is possible to use regular Boveda packs to calibrate a hygrometer if you’re in a pinch. For instance, your hygrometer might be giving you wild readings without any explanation. Therefore, you may need to quickly check it to see if it’s not the device that’s at fault.
Should you take this approach, it’s important that you use a brand new Boveda pack to avoid any possible anomalies. Furthermore, it’s imperative that this is undertaken in an air-tight seal. A regular zip-lock bag or humidor will likely give some humidity exchange.
Consequently, we recommend either a small Boveda bag or a quality tupperdor. We really like Sistema’s Klip-It containers as they offer the best air-tight seal you can get. Furthermore, ensure that whatever container you use is as small as possible so that the Boveda pack can fully humidify it.
As with the process described above, you will then simply have to wait 24 hours for the hygrometer’s readings to stabilise. Once this time has elapsed, you can make the necessary changes to your device.
While this process is absolutely fine, it might cost a touch more than the calibration kits if you have to purchase the packs and containers. This is especially the case if you want to do a two-step calibration as described above.
Why You Shouldn’t Calibrate A Hygrometer Using The Salt Test
One of the most practised methods for calibrating a hygrometer is known as the “salt test”. This essentially consists of placing the hygrometer in an airtight container with salt diluted in distilled water, which supposedly creates an environment of 75% RH.
A typical salt test requires the following:
- Bottle cap
- Distilled Water
- Pure Salt
- Airtight Container
Meanwhile, a salt test consists of the following steps:
- Place an empty bottle cap in an airtight container.
- Fill the cap with pure salt.
- Add just enough water for the salt to dissolve.
- Add the hygrometer and seal the container for 24 hours.
- Adjust the hygrometer as described below to 75%.
Again, try to opt for the smallest container possible and ensure that it has an air-tight seal. Nevertheless, we’re not overly confident with this method. Although it’s reasonable for getting an estimation of the hygrometer’s accuracy, it’s not very reliable for obtaining precise methods.
Firstly, the resulting humidity level is highly dependent to the surrounding temperature and can vary wildly. Furthermore, there are lots of varieties of salt, which each have their own characteristics due to impurities and crystal size. Similarly, using different amounts of water may also give you different results.
Some people may argue that any quantity of water evaporated by salt will produce the same humidity level. Additionally, they may suggest that all salt is simply sodium chloride and will behave the same way.
However, domestic NaCl is often fortified with micronutrients including Potassium Iodate, Sodium Ferrocyanide, Sodium Aluminosilicate, and Magnesium Carbonate. Unless you work in a laboratory, it may also contain trace amounts of metals such as aluminium and arsenic.
Finally, there’s no guarantee how well the humidity will distributed in the container. Likewise, the salt and water will simply emit moisture whereas a Boveda pack is designed to absorb excess amounts.
For these reasons, we prefer using the Boveda method listed above. Not only is it considerably more accurate but it’s not as messy and still quite affordable.
How To Adjust & Calibrate A Hygrometer
Hygroset II Digital Hygrometer Adjustment
As you’ve probably read above, there are a number of methods to calibrate a hygrometer, which can yield different results. Yet, how to you adjust the reading on the hygrometer itself?
Firstly, this is assuming that your hygrometer can be calibrated. Some cheaper digital models don’t come with this feature and we generally don’t recommend buying them.
That said, Xikar’s Purotemp hygrometer is surprisingly accurate despite not coming with this feature. Nevertheless, we prefer the option so we can periodically tune our hygrometers and make sure that they’re accurate.
In all cases, the hygrometer should come with a dial or something that can be adjusted after it has been exposed to a specific humidity level. Presuming that this was in a Boveda 75% calibration kit, you simply need to turn it until it reads 75%.
After that, it should be accurate at all other levels. Nevertheless, you can always perform Boveda’s two-step calibration to make doubly sure!
Analogue Hygrometer Adjustment
Most quality digital hygrometers allow you to do this quite easily by turning a dial on the front or back. Likewise, analogue hygrometers will often feature a screw on their rear, which turn the needle to the desired level.
Smart sensors are a little different in this respect. In the case of the Boveda Butler, the calibration process is automatic when using their kits as the app has an in-built wizard.
Boveda Butler App Calibration Wizard
As for Sensor Push and Cig Sor, they don’t always have in-built processes. Sometimes, you simply use the app to tell it to read a few points higher or lower. The benefit of this is that you aren’t forced to follow a 24-hour process. However, you aren’t accompanied by an in-app tool either.
Cig Sor App Calibration [Left], Sensor Push [Right]
How Often Do You Need To Calibrate A Hygrometer?
Even with the most premium and accurate hygrometer in the world, calibration is not just a one-step “set it and forget it” process. In fact, it’s highly recommended that you periodically re-calibrate it.
Much like an engine or a musical instrument, hygrometers require tuning, and the necessary frequency depends on the technology under the hood.
For instance, analogue hygrometers are made from hair fibres and springs. Consequently, they will soon fall out of sync and require a new calibration process. In fact, this is another reason that we’re not particularly fond of them as it makes them even less reliable.
If you do prefer to use an analogue hygrometer, we suggest re-calibrating it at least every six months.
Meanwhile, digital hygrometers tend to last a lot longer between calibrations. While you could potentially use one for years without any issues, we would recommend that you make it a yearly maintenance routine.
In most cases, you’ll have to set yourself a reminder. However, Boveda’s app lists the date of your previous calibration so it’s quite convenient.
What Next?
Now that you’ve learned how to calibrate a hygrometer, why don’t you also check out our related guides below:
- BU Cigars – Home
- Best Hygrometers For Humidors
- Best Wooden Humidors To Buy Online
- Top Cigar Coolers For Your Home
- How To Build Your Own Humidor
Alternatively, watch our video on why and how to calibrate a hygrometer!
"Fantastic guide, well done. My hygrometer was all over the place so this guide was a massive help!"Rating: 5.0 ★★★★★
Cigars Contents
My salt must be very good because I always have 75% :) , for comparison boveda always 77%, but based on their website it is correct “ACCURACY:
In an airtight environment, all Boveda are accurate to +/- 2% of the RH printed on the pack.”
Your salt test instructions are wrong. You shouldn’t dissolve the salt in water. You just add enough to make a thick paste. I’ve done it that way for years, and it is accurate enough for my uses.
The salt test instructions we’ve provided here are what has worked for us, though I suppose there’s more than one way to do it.
Rafael
There are some fine points to using salts for calibration, but unless you are calibrating at low humidity levels, as is the case with magnesium chloride, discrepancies are minimal. NaCl will indeed draw humidity from the air to achieve 75%. Salts will equilibrate with the environment until stable, whether releasing or absorbing water vapor. NaCl produces a stable humidity over a wide temperature range, from 0 to 45 degrees C, so temperature control is hardly critical. Minute traces of other substances is unlikely to affect the achieved humidity. For a list of different salts, temperatures and humidity levels, refer to the 1977 paper “Humidity Fixed Points of Binary Saturated Aqueous Solutions”, available online.
I also doubt that a sealed baggie will leak sufficient vapor to make a difference, but I would still use a freezer bag instead of a sandwich bag since they are much thicker and much more resistant to vapor leakage.
I also question that calibration using two widely separate points (33% and 75%) is of any value. One calibration will simply undo the other. There is no way to shift separate sections of the response curve of a hygrometer. Better would be to find an appropriate (non-caustic) salt near the humidity of interest and calibrate to that level. Then you can be confidant that at the target humidity, the meter will be close even though it might still be off when the humidity is significantly different.