Hygrometers: Essential Tools

Hygrometers: Essential Tools for Managing Indoor Humidity (Australia)

Too damp or too dry air can cause health issues, mould, damaged finishes and cranky HVAC systems. A simple hygrometer shows your indoor relative humidity (RH) so you can keep it in the comfort “Goldilocks” zone.

What Is a Hygrometer?

A hygrometer measures relative humidity—how much moisture is in the air compared with the maximum the air can hold at the current temperature. Readings are shown as a percentage (%).

How It Works (Plain English)

  • Digital (capacitive/resistive sensors): An electronic sensor changes value as moisture changes; a microchip converts this into %RH.
  • Psychrometer (wet/dry bulb): Two thermometers—one wrapped in a damp wick—are compared. The temperature difference (“wet-bulb depression”) is used with a chart to find %RH.

What They Measure & Ideal Indoor Ranges

  • Relative Humidity (RH): Comfort range is typically 40–60% indoors.
  • Risks: >60% = mould, mites, swollen timber. <40% = dry skin, static, irritated airways.

Types at a Glance

Type Best for Pros Watch-outs
Digital handheld / desktop Homes, offices, greenhouses Fast, easy to read, often logs temp + RH Calibrate/check accuracy yearly
Bluetooth/app-enabled Monitoring multiple rooms or remote checks Graphs, alerts, easy sharing Keep away from vents/steam for best accuracy
Psychrometer (wet/dry bulb) Training, field verification No batteries, reliable method Needs chart and proper technique
Testo 610 pocket hygrometer measuring indoor humidity

How to Read a Hygrometer

Digital: Place the unit about 1–1.5 m above the floor, away from vents, windows and steam. Wait 2–3 minutes for the reading to stabilise.

Psychrometer: Measure dry-bulb and wet-bulb temperatures, calculate the difference, then use a psychrometric chart to find %RH.

  • Dry-bulb temperature
  • Wet-bulb temperature
  • Wet-bulb depression = dry-bulb − wet-bulb

Calibration: Quick “Salt Test”

  1. Add a teaspoon of table salt to a bottle cap, moisten (not dissolve).
  2. Place cap and hygrometer in a sealed food container for 8 hours at room temp.
  3. The air in the container should be ~75% RH. Adjust the calibration screw to 75%, or note the offset if your model can’t be adjusted.

Tip: Check calibration every 6–12 months. Analogue units drift more and need more frequent checks.

Testo 625 digital thermohygrometer tracking indoor humidity and temperature

Benefits at Home & Work

  • Health: Reduce mould and dust mites at high RH; ease dryness at low RH.
  • Comfort: Balance humidity so rooms feel cooler in summer and warmer in winter.
  • Protection: Help prevent warped timber, peeling paint and corrosion.
  • Plant care: Keep greenhouses and indoor plants in the right RH band.
  • HVAC efficiency: Optimise dehumidifiers/humidifiers and airflow settings.

Shop Hygrometers

Explore handheld, Bluetooth and pro thermohygrometers: Browse hygrometers →

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