Last Updated on October 25, 2026 by Umar Farooq
Hygrometer vs humidistat in one line: a hygrometer only measures and displays humidity; a humidistat measures it too, but then switches equipment on or off to hold a target. One is a gauge, the other is a gauge wired to a switch.
If you have ever set a dehumidifier to 50% and then wondered why a separate hygrometer in the same room says 56%, you have met both in one living room. They are not rivals. They are different jobs that happen to share a sensor.
Hygrometer vs humidistat in one line each
A hygrometer is the thing you look at. Wikipedia’s entry on the humidistat says it plainly: a hygrometer only measures humidity, while a humidistat “has the functionality of a switch”, and humidistats employ hygrometers but are not the same.
So a humidistat contains a humidity sensor, compares it with a set point, and acts. It is a thermostat that has switched its interest from temperature to moisture. Meaco’s explanation of what a humidistat is uses exactly that comparison: set 50 %rh and the dehumidifier stays off below that level and runs above it.
| Hygrometer | Humidistat | |
|---|---|---|
| Measures humidity | Yes | Yes |
| Shows you a number | Always | Sometimes, sometimes only a dial or setting |
| Switches equipment | No | Yes |
| Also called | Humidity meter, thermo-hygrometer (with temperature) | Hygrostat |
| Found in | Standalone gadgets, weather stations | Dehumidifiers, humidifiers, some extractor fans |
Where you will actually meet a humidistat
Mostly inside something. A dehumidifier’s built-in control is a humidistat, which is why what a humidistat on a dehumidifier does is a question of its own. Some bathroom extractor fans carry one too, which is the idea behind humidity sensor extractor fans.
Notice what these have in common: the sensor is not there to inform you, it is there to decide. Sometimes the only evidence you get is that the machine went quiet.
Why a built-in humidistat is not a substitute for a hygrometer
Three reasons, in order of how often they bite.
- It sits inside the machine. The sensor reads the air that reaches the machine, which is not necessarily the air in the middle of the room. The general point that a reading depends on where the sensor sits is made by the National Physical Laboratory, whose humidity measurement guide warns that measuring at a cold spot can over-estimate the typical humidity in a room.
- It tells you a setting, not a reading. A dial marked 1 to 10 is a target, not a measurement. A digital panel shows a number, but I would not call it a precision instrument, and the settings guide explains why.
- It cycles. A humidistat is designed to swing around its target, so what it displays at one moment is not the humidity of the room all day.
A £10 standalone hygrometer on the far side of the room is a cheap second opinion. Where to put it is covered in where to put a hygrometer.
Do you need a hygrometer, a humidistat, or both?
If the question is “what is my humidity?”, you need a hygrometer. Everything in the EPA’s brief guide to mould and moisture about keeping indoor humidity below 60 per cent, ideally 30 to 50 per cent, is checked with one.
If the question is “how do I keep it there without standing over it?”, you need a humidistat, which in a home means a machine that has one built in.
Most damp households want both, and they are not interchangeable: the hygrometer is how you judge whether the humidistat’s setting is doing what it should. For the reading side, how to read a hygrometer is the starting point.
A hygrometer tells you, a humidistat acts, and you want one of each
Use the hygrometer to find out, the humidistat to maintain, and do not assume the humidistat has already told you the truth. A machine that has reached its target and gone quiet has proved only that its own sensor is satisfied.
FAQ
What is the difference between a hygrometer and a humidistat?
A hygrometer measures and displays humidity. A humidistat measures it and also switches equipment such as a dehumidifier on or off to hold a set level.
Is a humidistat the same as a hygrostat?
Yes, hygrostat is another name for the same device, according to Wikipedia.
Can a humidistat replace a hygrometer?
Not reliably. It reacts to the air at its own sensor and often shows only a set point, so a separate hygrometer is a better way to check the room.
Does a dehumidifier have a hygrometer in it?
It has a humidity sensor, which is the measuring part of its humidistat. That does not mean it displays a trustworthy reading, so treat the panel figure as a guide.
Which do I need to monitor mould risk?
A hygrometer. Mould risk follows the humidity of the room over time, and a log of readings is more useful than a switching control.
