A hygrometer is an instrument that measures humidity, the amount of water vapor in the air, and most models show it as relative humidity in percent. In a cigar humidor it tells you whether your cigars sit in Boveda's recommended 65 to 72% range. Analog dials read a hair or fiber element; digital models read an electronic sensor.
What is a hygrometer?
Britannica defines a hygrometer as a meteorological instrument for measuring humidity, meaning the water vapor carried by the air. Most display relative humidity, or RH, which the American Meteorological Society's glossary describes as the ratio of the air's actual vapor pressure to its saturation vapor pressure, usually given as a percentage. In plain terms, 70% RH means the air holds about 70% of the water vapor it could hold at its present temperature, so warming or cooling the same air changes the reading.
Britannica also covers designs used outside the humidor, such as the wet-and-dry-bulb psychrometer and the chilled-mirror dew-point hygrometer. Cigar humidors rely on the dial and digital types below.
How does a hygrometer work?
How analog hygrometers work
Analog hygrometers use materials that lengthen and contract with humidity. Britannica lists goldbeater's skin (ox gut) and human hair; their movement works a spring that turns the needle. According to humidity course material on the Japan Meteorological Agency's website, hair grows 2 to 2.5% longer as RH climbs from 0 to 100%, and its length change on rising humidity is 5 to 6% larger than on falling humidity. That effect, called hysteresis, means a dial's reading can depend on whether the air has been getting wetter or drier. Some dials use synthetic hair: when Cigar Aficionado reviewed one in October 2012, its tester found it read within about one point of the actual RH.
How digital hygrometers work
In a capacitive sensor, the World Meteorological Organization's instrument guide explains, a thin polymer film sandwiched between electrodes takes up water as RH rises. The water alters the film's dielectric properties, the capacitance shifts, and the electronics turn that into a number. A resistive sensor tracks electrical resistance instead; Britannica describes designs built on a thin lithium chloride layer or a semiconductor. In a June 2020 bench test, Zurich Instruments application scientist Meng Li found a capacitive sensor recovered from a humid blast in about 10 seconds against roughly 100 for a resistive one.
Analog vs digital hygrometer: which is more accurate?
Neither type is accurate by default; what counts is whether your unit has been checked. The meteorological figures below compare the sensing principles, not any one consumer product.
| Feature | Analog (hair or fiber dial) | Digital (electronic sensor) |
|---|---|---|
| Sensing element | Hair or another material that changes length (Britannica) | Polymer film whose capacitance changes, or a layer whose resistance changes (WMO, Britannica) |
| Hysteresis | Hair's length change is 5 to 6% larger on rising than on falling humidity (JMA) | Within 1% RH between 60 and 80% RH, capacitive (JMA) |
| Benchmark | Treated as faulty if it averages 5 points or more off a reference over 10 days (JMA) | Within 1% from 0 to 90% RH once calibrated, capacitive (JMA) |
| Weak points | Zero shifts, contamination, hysteresis (WMO) | Drift, mostly upward at high humidity; contamination (WMO) |
| Calibrate | At least every six months (Bespoke Unit, Boveda) | Yearly (Bespoke Unit); every six months (Boveda) |
Five points covers most of Boveda's 65 to 72% target band, so the error matters. Bespoke Unit, a lifestyle publication that covers cigars, says hair-and-spring dials fall out of sync sooner, digital units hold calibration longer, and inexpensive digital models that cannot be adjusted are worth skipping.
Why does a cigar humidor need a hygrometer?
According to Boveda, cigars kept below 65% RH dry out, lose flavor, burn fast and can crack, while above 72% they turn spongy, burn unevenly, can split, and risk mold. Boveda adds that wood humidors can lose 2 to 5% RH, and that a humidor often settles up to 5 points under its pack's rating, depending on the box and how dry the room is. A hygrometer shows you that gap.
If your humidor holds Opus X cigars, Padrón cigars or Liga Privada No. 9 cigars, a calibrated reading tells you when conditions move. Some humidors build a gauge in: the Colibri Quasar Humidor, which holds 40 to 45 cigars, includes a digital hygrometer. See our cigar humidors.
What humidity should cigars be kept at?
Boveda puts the target between 65 and 72% RH, and Cigar Aficionado's glossary advises aiming for about 70 percent. Boveda matches its pack levels to the container and to taste:
- 65%: a drier profile and easier burn, suited to long-term aging and, Boveda says, to Cuban cigars.
- 69%: the level Boveda calls most preferred for premium cigars, for airtight humidors, tupperdors and humidor bags. See the Boveda 69% pack.
- 72%: for most wood humidors and drafty or dry rooms. See the Boveda 72% pack, or the Boveda 8 gram 72% for small containers.
- 75%: for inexpensive or glass-top humidors and extremely dry settings, desert environments among them; not for airtight containers. See the Boveda 75% pack.
- 84%: only for seasoning an empty wood humidor.
Our Boveda pack guide compares the levels in more depth.
How do you calibrate a hygrometer?
Calibrating a hygrometer means exposing it to air at a known RH, comparing its reading, then adjusting the gauge or noting the offset.
The salt test
Air sealed over saturated table salt settles at a predictable humidity. Lewis Greenspan of the National Bureau of Standards, now NIST, published reference values in 1977: about 75.5% RH at 20°C (68°F) and 75.3% at 25°C (77°F). The Museum of Fine Arts, Boston explains why: in a closed space the liquid releases vapor when the air is dry and the undissolved salt absorbs moisture when it is humid.
- Fill a bottle cap with plain salt and add water a few drops at a time until it is wet through, leaving some crystals undissolved.
- Set the cap and the hygrometer in the smallest airtight container you have; Bespoke Unit stresses a tight seal.
- Leave it closed for 24 hours at a steady room temperature. The WMO cautions that salt systems are reliable only once fully equilibrated to the surrounding temperature.
- Read the gauge. At 75% it is on target; at 72% it runs 3 points low.
- Adjust the gauge if it allows it, or note the offset and apply it to later readings.
The Boveda calibration kit
Boveda's One-Step 75% Hygrometer Calibration Kit is a resealable bag with a 75% RH pack. Seal the hygrometer inside for at least 24 hours at 65 to 75°F and expect 75%; if it differs, note the margin or adjust, then repeat. Boveda says the bag can be reused within three months. A 32% kit checks the low end, so using both gives a two-point calibration.
How often should you calibrate a hygrometer?
Boveda advises every six months, since gauges drift. Bespoke Unit suggests at least every six months for analog dials and yearly for digital units. Test sooner whenever a reading jumps without explanation.
Where should a hygrometer go in a humidor?
Mind the heat. The WMO guide notes that radiant heat can warm a sensor above the surrounding air and produce a falsely low RH, and the Japan Meteorological Agency material puts the error near 3% for each 1°C of difference at 20°C and 50% RH. Mount the hygrometer inside the closed humidor where you can read it, and keep the humidor out of direct sun and away from lamps, vents and warm electronics.
Our product notes suggest letting a hygrometer settle for a few days in a freshly humidified humidor before loading cigars, then checking it weekly. Travel cases need care too: Fuente Aged Selection notes that the Opus6 Travel Humidor does not include a humidifier.
Hygrometer troubleshooting: why is my reading off?
- Wild swings. Bespoke Unit suggests sealing the gauge with a fresh Boveda pack in an airtight container for 24 hours. If it settles near the pack's rating, look at the humidor; if not, the gauge is at fault.
- Low in a wood humidor. Boveda recommends 72% for most wood humidors and 75% for inexpensive or glass-top boxes.
- Reading high. Boveda packs absorb moisture as well as add it, which sponges, beads and gels do not. Boveda also says not to mix RH levels or combine its packs with other humidifiers.
- Moves when the room warms. RH depends on temperature, so check at a similar time each day, away from heat.
- Not adjustable. Record the difference from 75% and correct each reading by it, as Boveda's instructions allow.
- Reused calibration bag. Bespoke Unit says used packs are less accurate for later calibrations.
Hygrometer FAQ
What does a hygrometer do in a cigar humidor? It shows the relative humidity inside the box, so you can confirm your cigars sit in the 65 to 72% range Boveda recommends before they dry out or turn spongy.
How do you calibrate a hygrometer with salt? Seal it in a small airtight container with a bottle cap of damp table salt for 24 hours at a steady room temperature, then compare the reading with 75%. Adjust the gauge or note the difference.
How often should I calibrate my hygrometer? Boveda recommends every six months. Bespoke Unit suggests yearly for digital gauges and at least every six months for analog dials.
Is a digital or analog hygrometer more accurate? Neither is accurate by default. Bespoke Unit says digital gauges tend to hold calibration longer than analog dials, but any gauge should be calibrated before you rely on it.
What humidity should a cigar humidor be? Boveda recommends 65 to 72% RH and calls 69% the most preferred level for premium cigars; Cigar Aficionado suggests about 70 percent.
Where can I buy Boveda packs and humidors in Yuma, AZ? At Sun of a Gun Cigars & Spirits, 1651 S Arizona Ave in Yuma, an official J.C. Newman Diamond Crown Cigar Lounge. Call 928-276-3500, or order Boveda packs online.
Sources
- Britannica: Hygrometer
- AMS Glossary: Relative humidity
- WMO: Measurement of Humidity (2018)
- Japan Meteorological Agency: Measurement of Humidity
- Zurich Instruments: Resistive or Capacitive?
- Greenspan, NBS (1977): Humidity Fixed Points
- MFA Boston CAMEO: Saturated salt solutions
- Boveda: What's the RH for cigars?
- Boveda: Which RH for my cigars?
- Boveda: RH for tobacco
- Boveda: How do I calibrate my hygrometer?
- Boveda: 75% calibration kit
- Boveda: 32% calibration kit
- Cigar Aficionado: Humidification element
- Cigar Aficionado: Adorini Hair Hygrometer
- Bespoke Unit: Calibrating a hygrometer
For the full picture on keeping cigars, read how to store cigars and our cigar humidor guide, or shop Boveda humidity packs. $9.99 flat shipping, free on orders of $125 or more.
