Humidity Meter aka Hygrometer - Analog vs Digital and How To Use Them - Red Eyes Online

Humidity Meter aka Hygrometer – Analog vs Digital and How To Use Them

 Hygrometers - analog and digital

Indoor growing is a science – you can’t just give your cannabis plants some water and led grow lighting and expect them to grow.

Light, water, and soil nutrients need to be carefully monitored to ensure the best results. Another factor you shouldn’t neglect in your grow tents is humidity.

Too much humidity can lead to mold growth and bud rot, rendering your cannabis completely unusable.

But when humidity levels are too low when your plants are young, they may not receive enough moisture to grow at all. Balance is the key.

What is a Hygrometer?

A hygrometer is an instrument that measures the amount of water vapor in a given space, better known as humidity.

The higher the humidity, the warmer and wetter it feels – the lower the humidity, the colder and drier it feels.

Two rooms at the exact same temperature can feel completely different if their humidity levels are different.

Humidity affects how much moisture your plants receive and absorb, which is why hygrometers and grow tents go hand in hand.

Seedlings and plants in the early stages of growth prefer higher levels of humidity compared to mature plants.

How to Read a Humidity Meter

A hygrometer measures both the temperature and the amount of water vapor in a room to calculate relative humidity, which appears as a percentage.

How to Read a Humidity Meter

So if your hygrometer reads 30%, that means that there is 30% of the maximum amount of water vapor that can be present at that temperature.

The higher the temperature, the greater the maximum humidity. The lower the percentage, the lower the relative humidity – the higher the percentage, the higher the relative humidity.

Once you’ve calculated the humidity of the room your grow box is in, you can use a humidifier or a dehumidifier to adjust accordingly.

Cannabis plants prefer high humidity (70%) as seedlings and lower humidity (40%) as they began to sprout, grow, and flower.

The humidity for flowering plants should be below 40% to prevent mold growth.

Types of Hygrometers

There are two main types of hygrometers – mechanical and digital. Both have their own advantages and disadvantages, but digital hygrometers are more commonly used for indoor growing.

Mechanical Hygrometers

Mechanical hygrometers display relative humidity on a gauge. While usually more aesthetically pleasing, they’re generally less accurate and more difficult to read than digital hygrometers.

The only real advantage mechanical hygrometers have over their digital counterparts is that they don’t require batteries.


A psychrometer is a type of mechanical hygrometer that uses two thermometers, one dry bulb and one wet bulb, to measure humidity.

The dry bulb measures the temperature of the air while the wet bulb measures liquid temperature.

By comparing these two readings, a psychrometer is able to calculate and display the room’s relative humidity.

A psychrometer reading is far more accurate than a standard household mechanical hygrometer reading.

Digital Hygrometer

Easy to read, highly accurate and relatively inexpensive, digital hygrometers are the most popular way to measure relative humidity.

Digital Hygrometer

They’re able to record and keep track of fluctuations in humidity so that you can see if there were any major changes while you were out of the house.

Many come with additional bells and whistles such as an alarm system, clock, and backlighting.

Top 5 Hygrometers

Along with the best LED grow lights, a good hygrometer is essential to successful indoor growing.

To help you better tend to your grow box, we’ve put together a short list of the top 5 hygrometers:

SensorPush Wireless Thermometer/Hygrometer for iPhone/Android

The SensorPush is a wireless thermometer and hygrometer that uses a free downloadable app to transmit data to your smartphone, alerting you whenever there’s a shift in humidity.
SensorPush Wireless Thermometer/Hygrometer for iPhone/Android
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  • Bluetooth Alerts: You don’t need to worry about constantly checking the reading on your hygrometer – updates are sent straight to your phone through Bluetooth.
  • Cost: While it isn’t expensive at $50, the SensorPush is more expensive than most hygrometers.
  • Constant Monitoring: The sensor is always collecting data, so you can see changes in humidity and temperature over time in the form of a graph using the app.

ThermoPro TP55 Indoor Thermometer and Humidity Monitor

This digital hygrometer is battery powered and backlit so that it can be seen in the dark. The humidity reading is updated every 10 seconds, and the ThermoPro’s touchscreen allows for easy adjustment.
ThermoPro TP55 Indoor Thermometer and Humidity Monitor
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  • Easy to Use: The touchscreen, magnetic backing, large display, and backlighting make the ThermoPro easy to use and read.
  • Backlight is on a Timer: The backlight only comes on when the hygrometer’s touch screen is pressed, then goes away after a few seconds. So even though it’s backlit, you can’t see the humidity level from across a dark or dimly lit room.
  • Humidity Tracking: Screen displays temperature and humidity highs and lows of the last 24 hours.

Habor Portable Hygrometer

Small and versatile, this hygrometer is great for anyone looking for something simple, affordable, and accurate.
Habor Portable Hygrometer
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  • Versatility: The hygrometer can be mounted on a wall, stuck to a magnetic surface, or stood up on a flat surface using the kickstand.
  • No Backlight: The Habor hygrometer can’t be read in the dark at all.
  • Simple: If you don’t like fussing with buttons and settings, this is the hygrometer for you. Only shows the current temperature and relative humidity level with one button for changing from Fahrenheit to Celsius.

Moost Temperature & Humidity Monitor with Alarms

This hygrometer from Moost accurately measures relative humidity and temperature and displays them on a digital screen.
You can view the highest and lowest readings of the last 24 hours, allowing you to keep track of major fluctuations.
Moost Temperature & Humidity Monitor with Alarms
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  • Easy to Read: The Moost hygrometer not only shows humidity as a percent, but also on a gauge so that you can quickly see if the room is too dry or too moist.
  • Alarm: The alarm feature is slightly misleading – it features an alarm clock, not an alarm to notify you when the humidity has gotten too high or too low.
  • Stylish and Simple: Available in both black and white, the Moost hygrometer looks nice in any room. It can stand on flat surfaces or be mounted to a wall.

AcuRite 01083M Pro Accuracy Temperature & Humidity Monitor

Another great option for indoor growing, the AcuRite hygrometer has a large, easy to read humidity and temperature display and is highly accurate.
AcuRite 01083M Pro Accuracy Temperature & Humidity Monitor
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  • Frequent Updates: The AcuRite hygrometer updates and displays the current temperature and humidity every 10 seconds.
  • No Clock: Displays humidity history on a 24-hour cycle, but the lack of an adjustable clock means that the cycle begins when the batteries are inserted.
  • High Accuracy: The margin of error for temperature is 0.5 degrees Fahrenheit and only 2% for relative humidity.

Photos from: amphoto /, nuttawutnuy /, VIPDesignUSA /

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