How to Calibrate a Cigar Hygrometer: The Salt Test and the Boveda Kit

Affiliate disclosure: As an Amazon Associate, The Next Cigar earns from qualifying purchases. We earn a small commission on purchases made through these links, at no extra cost to you.

Every decision you make about a humidor (add water, swap a pack, open the lid, leave it alone) rests on one number: the reading on the hygrometer. If that number is wrong, every decision after it is wrong too.

Hygrometers drift. Boveda, which makes a widely sold calibration kit, says both analog and digital units do, and that even a freshly calibrated hygrometer is only accurate to about ±3–5% RH. That is why the job is not “buy a good hygrometer” but “check the one you have, and keep checking it.”

The good news: checking it takes a sandwich bag and some table salt, or an $8 pouch. Here is how.

Why 75% is the magic number

Both methods below rely on the same bit of physics. Seal a damp paste of ordinary salt (sodium chloride) in a small airtight space, and the air above it settles at a fixed relative humidity. That value was measured precisely by the US National Bureau of Standards (now NIST) in a 1977 paper by Lewis Greenspan, which is still the standard reference:

Room temperature	Table salt	Magnesium chloride
15 °C	75.6% RH	33.3% RH
20 °C	75.5% RH	33.1% RH
25 °C	75.3% RH	32.8% RH
30 °C	75.1% RH	32.4% RH

Source: Greenspan, “Humidity Fixed Points of Binary Saturated Aqueous Solutions”, J. Res. NBS 81A (1977), Table 2.

The salt column barely moves across normal room temperatures, which is what makes it useful: at home, a saturated salt test reads 75%, whether your flat is chilly or warm. (The magnesium chloride column is the second reference point, for later.)

The Boveda calibration kit is the same idea in a sealed, ready-made pouch: Boveda states it is a 75% RH environment.

Method 1: the salt test

This is the method in the set-up instructions that UK humidor retailers C.Gars and Simply Cigars ship with their humidors.

You need: table salt, water, a bottle cap or small cup, and a large resealable freezer bag.

1. Make the paste. C.Gars uses about ½ cup of salt and ¼ cup of water. For a small bottle cap, just dampen a capful of salt. The salt should not dissolve: you want “the consistency of wet sand”, with no water pooling on top.
2. Bag it. Put the cap or cup in the freezer bag, and the hygrometer next to it. The salt must not touch the hygrometer.
3. Seal it completely. A bag that leaks will never reach 75%.
4. Leave it alone at a steady room temperature, away from drafts, direct sun and heating or cooling vents.
5. Wait. Published times vary: Madelaine’s hygrometer instructions say 4 hours, C.Gars and Simply Cigars say 8–12 hours, Boveda says at least 24 hours for its kit. A longer wait does no harm, so if you can, leave it overnight and check the next day.
6. Read it through the bag. C.Gars warns that the reading drops quickly once the hygrometer meets dry room air. Do not take it out to look.

It should read 75%. Write down what it actually reads.

Method 2: the Boveda 75% kit

The Boveda One-Step Calibration Kit replaces the salt and water with a sealed humidity pack inside a resealable bag. Boveda’s instructions:

1. Put the hygrometer in the kit’s bag with the pack and reseal it fully.
2. Wait at least 24 hours, at a room temperature of 65–75 °F (about 19.5–23.5 °C).
3. If it reads 75%, you are done. If not, adjust the hygrometer to 75%, or note the difference, then repeat the test with the same kit to confirm.

Once opened, Boveda says the kit is good for three months (put the pack back in its bag between uses); unopened, up to two years.

Which method? Both target the same 75%. The salt test costs nothing. The kit avoids mixing, mess and the risk of wet salt touching the hygrometer, and gives you a sealed, repeatable test you can redo after an adjustment. If you calibrate more than one hygrometer or plan to check every few months, the kit is the easier habit.

Adjusting the reading

What you do next depends on your hygrometer.

Analog dial. Some dials have a small adjustment screw or wheel on the back. The humidor instructions above say to turn it so the needle reads 75% while it is still in (or straight after) the test. Then put it back in the bag and repeat the test to confirm. If yours has no screw, do not force it: use the offset method below.

Digital with a reset button. Some digital units, such as the Madelaine adjustable hygrometer, are reset to 75 by pressing and holding a button through the bag at the end of the test. Check your model’s manual.

Govee H5075 and other app-based units. Govee rates the H5075 at ±3% RH, and the Govee Home app has a humidity calibration setting (Govee publishes a help article on it). Enter the difference you measured, so a unit that read 72% in the test gets +3.

No adjustment at all: use an offset. Write the correction on a piece of tape on the back. If it read 72% in a 75% test, add 3 to every reading: when it shows 62%, your humidor is at about 65%.

If your hygrometer reads more than a few points off, or drifts again within weeks, it may not be worth correcting. A digital unit that reads within its rated tolerance is cheaper than a ruined box.

How often to check

• Every new hygrometer, before first use. Boveda says to do this even for units sold as “pre-calibrated”.
• Then every six months (Boveda), or at least yearly (C.Gars).
• Whenever a reading surprises you. A sudden jump or drop is as likely to be the hygrometer as the humidor.

The mistakes that ruin the test

Each one of these comes from the makers’ instructions:

• Too much water. You want wet sand, not salty water.
• Salt touching the hygrometer. It can damage the unit and spoils the reading.
• A bag that isn’t sealed. Press out the air and check the seal along its full length.
• A drafty or changing spot. Window sills, radiators and air-conditioning vents swing the temperature, and humidity readings move with it.
• Reading too soon. Give it at least the full time; overnight is safest.
• Taking it out to read it. The number falls within seconds in dry room air.

Going further: a two-point check

A single test tells you whether the hygrometer is right at 75%. It does not tell you whether it is right at 65%, where your humidor actually sits. A second reference point near the bottom of the scale shows whether the error is the same across the range.

Saturated magnesium chloride gives about 33% (see the table above), and Boveda sells a 32% kit and a two-point (32% + 75%) kit for this. For most smokers, a regular 75% check is enough. A two-point check is worth it if you keep valuable boxes long term.

Why the number matters

Habanos S.A. says to store its cigars at 16–18 °C and 65–70% relative humidity, to keep the temperature steady because humidity moves with it, and never to let the humidor go above 18 °C because of the tobacco beetle. A hygrometer reading 5 points low can have you adding water to a box that is already too wet; one reading high can let cigars dry out while the dial looks fine.

For why we hold Cuban cigars at the bottom of that range, read how to store Cuban cigars: 65%, not 70%. If summer is pushing your numbers around, see the summer humidity survival guide. And if it’s time for a new box altogether, start with the best cigar humidors of 2026.

Quick answers

What should a hygrometer read in the salt test? 75%. NIST’s measurements put saturated salt at 75.1–75.6% between 15 and 30 °C.

How long should I leave it? At least 8–12 hours for the salt test; Boveda says at least 24 hours for its kit. Overnight or a full day is safest.

Can I reuse the Boveda kit? Yes. Reseal it, and it lasts about three months after opening.

How accurate is a calibrated hygrometer? Boveda says about ±3–5% RH. Govee rates the H5075 at ±3% RH.

How often should I calibrate? When it’s new, then every six months (Boveda) or at least once a year (C.Gars).

---

Sources: Greenspan, L., “Humidity Fixed Points of Binary Saturated Aqueous Solutions”, J. Res. NBS 81A(1), 1977 (nvlpubs.nist.gov); Boveda, One-Step Calibration Kit instructions and “Why do I need to calibrate a hygrometer?” (bovedainc.com); C.Gars Ltd and Simply Cigars humidor set-up instructions; Madelaine adjustable hygrometer instructions (Neptune Cigar); Govee H5075 specifications (govee.com); Habanos S.A., “Keeping Habanos” (habanos.com). Prices and ratings checked on Amazon.com on 21 October 2026.