What a hygrometer tells you

A hygrometer measures relative humidity, the amount of moisture in the air compared with the most it can hold at that temperature. It tells you whether wet windows and mould come from damp air or from cold surfaces, whether a dehumidifier is needed, and whether the changes you make are working. What the readings mean, and the range to aim for.

Where to get one

Hygrometers are cheap and easy to find. Amazon sells plenty (our picks are below), and DIY shops, garden centres and many supermarkets' home sections stock them too. A lot of digital room thermometers sold for nurseries and greenhouses show humidity as well, so check whether you already have one.

What to look for

  • Humidity and temperature on one screen. You need both, because the same humidity is riskier on a cold wall than a warm one.
  • A stated accuracy. Look for a figure in the listing, given as ± a percentage. The smaller it is, the more you can trust small changes in the reading.
  • Min/max memory. It records the highest and lowest readings since you last reset it, so you can see how humid the bedroom got overnight without being awake to check.
  • One per problem room. Humidity can be very different in a bedroom on an outside wall and a warm living room. A multi-pack lets you compare.
  • Logging, if you need a record. Bluetooth models save readings to a phone app as a graph. That is useful evidence if you are reporting damp to a landlord, and shows whether a room dries out during the day.

Our picks

These are chosen by their specs against the list above. We haven't tested them ourselves; the reasons say which spec puts each one here.

For most homes

TempPro TP50 Hygrometer Thermometer

Type
Digital
Accuracy
±3%
  • Min/max memory

Shows temperature and humidity with a stated accuracy of ±3%, and has a min/max memory so you can check the overnight peak in the morning. Enough to tell whether one room is too damp.

View on Amazon Manufacturer specs

For checking every room

TempPro TP49 Hygrometer Thermometer, 3-pack

Type
Digital
Accuracy
±3%
In the pack
3

3 hygrometers with the same ±3% accuracy, so you can put one in each bedroom and the bathroom and see which room is the problem. Using the same model everywhere makes the readings easier to compare.

View on Amazon Manufacturer specs

For a record of readings

Govee H5075 Bluetooth Hygrometer

Type
Bluetooth
Accuracy
±3%
  • Phone app

Logs readings to a phone app, so you can see a graph of the room over days or weeks. Its stated accuracy is ±3%. Pick this one if you want evidence for a landlord or want to see whether a dehumidifier is making a difference.

View on Amazon Manufacturer specs

Where to put it

  1. Put it at chest height on an inside wall, away from windows, radiators, the kettle and the bathroom door.
  2. Leave it for half an hour to settle after moving it.
  3. Read it at the same time each day. First thing in the morning, before you open a window, shows the room at its dampest.
  4. Reset the min/max memory each evening if you want to see the overnight peak.
Mould risk checker Put in your hygrometer's readings to see how close the room is to the point where mould grows.

If the readings stay high, see how to bring humidity down or work out what size dehumidifier you need.