How do I measure humidity in my home?
Use a hygrometer — a small device that displays relative humidity as a percentage. Basic digital hygrometers cost $15 to $30 in any Bunnings or Officeworks; smart Bluetooth versions cost $40 to $70 and log readings to your phone. Place one in the room you suspect, leave it for 24 hours, and read the high and low values. You now have data.
Where to put it
- Bedroom of anyone sleeping with the door closed
- Inside a wardrobe (especially if mould has appeared there before)
- Bathroom
- Laundry
- Living room
- Any room with persistent window condensation
Reading the numbers
Most digital hygrometers display current humidity as a percentage, with a high/low memory of the last 24 hours. The current reading tells you the moment; the high/low tells you the range. The high matters more for mould risk — a bathroom that hits 90% during a shower and drops to 55% within an hour is fine. One that hits 90% and stays above 70% for hours is not.
What the readings mean
| Reading | What's happening | What to do |
|---|---|---|
| Below 35% RH | Air is dry; static, cracking timber, dehydrated skin | Humidify; use indoor plants; tray of water near heater |
| 35–45% RH | Lower end of comfort; fine for most homes | No action needed |
| 45–60% RH | The comfort sweet spot | Maintain current habits |
| 60–70% RH | Moisture starting to accumulate; mildew risk | Ventilate daily; passive absorbers in closed spaces |
| 70–80% RH | Mould risk active; clothes and leather at risk | Electric dehumidifier in main rooms; absorbers everywhere |
| Above 80% RH | Mould will appear within weeks | Treat as urgent; identify and fix moisture source |
When and how often to check
Check at three points of the day for a week to build a baseline: first thing in the morning (highest in bedrooms), mid-afternoon (highest in living areas in summer), and last thing at night (highest in bathrooms after evening showers). After the first week, monthly spot checks are enough — until something changes (a new pet, new flooring, a renovation, a different season).
Related reading
- What's the right humidity level for an Australian home?
- The slow cost of leaving moisture alone in your home
- Why a fresh home feels different
