Mold Growth Humidity Chart: See How the Fungus Grows!

Checking a mold growth humidity chart is important if you live in a place that has high humidity, such as Seattle.

If you live in Florida where humidity creeps into the 90s in November, you will always be afraid of mold creeping in some space in your house.

And rightly so!

However, did you know that it does not take humidity alone for mold to grow? It takes these three things for mold to thrive:

  • Humidity/dampness/moisture
  • Nutrients – feeds on products made from plants or animals
  • The right warmth/temperature

In the past, we have looked at how temperature and humidity are related. Here, you can also see that mold needs both to thrive.

Mold growth humidity chart numbers

This chart is a rough preview to show you how soon mold is going to start developing in your home if there are certain temperature and humidity conditions:

Relative Humidity



Mold growth days




2 days to grow




3 days to grow




4 days to grow




6 days to grow




9 days to grow




40 days to grow




7 days to grow




8 days to grow




160 days to grow




330 days to grow




92 days to grow




216 days to grow




480 days to grow




Mold can't grow

You need to know at what humidity level mold will start to grow in your house. But that’s not all, because you also need to know at what temperature and dewpoint mold will grow.

Why are all these details important? You might wonder.

Mold is a dangerous indoor allergen. It causes many health effects, as you can see in our post on mold exposure symptoms in babies.

Long-term exposure to mold by inhaling it, ingesting it or via skin contact also causes serious mold toxicity symptoms in grown ups, and pets.

Mold growth humidity chart in Celsius

mold growth humidity chart

If you want to read the mold growth humidity chart in Celsius, you will just have to convert the dew point temperature in the above table from degrees Fahrenheit to degrees Celsius.

To convert degrees Fahrenheit to degrees Celsius, just subtract 32 from the given figure and then multiply the result by 5/9 (or 0.5556).

In the case of 95% relative humidity level, temperature at 80 degrees Fahrenheit and dewpoint at 78 degrees Fahrenheit, this will be 95% RH, 26.6 degrees Celsius, 25.5 degrees Celsius and in such conditions, mold will grow in 2 days.

You will also have to do the same for the temperature readings. The relative humidity level is expressed in percentage so that does not change.

Will mold grow at 70 humidity?

Will mold grow at 70 humidity

Mold might or might not grow at 70 humidity depending on the conditions present.

For instance, if the relative humidity is 70%, the indoor temperature is at 70°F and the dew point temperature is 60°F, mold will grow in about 160 days.

Compared to a situation where the relative humidity level is 95%, temperature is 80°F and dewpoint temperature is 78°F, mold will grow fast, in 2 days.

From the information above, you can deduce that mold will grow when the relative humidity is high, the indoor room temperature is high and the dew point temperature is high.

While the dewpoint and temperature might not be good for mold growth, 70 percent humidity level is still very high for you.

It will make you damp on the skin and uncomfortable. Besides, since there is heat indoors, it will make the air more uncomfortable.

If the humidity level exceeds 60 percent, comfort is out. You will experience all the effects of high humidity on the body.

Therefore, it is not just the mold you have to worry about, but your comfort and that of the pets as well.

Minimum humidity for mold to grow – 60%

Minimum humidity for mold to grow

If you check our mold growth humidity chart, you can tell the minimum humidity for mold to grow in your house.

For mold to grow in a few to several days, the temperature and relative humidity level have to be high.

For instance, mold will grow in 4 days if the relative humidity level is 89%, temperature is 65°F and dew point temperature is 61°F. If these conditions are higher than that, mold will grow fast in 2 to 6 days.

If the dew point temperature of a place is 55°F, relative humidity level is 80% and temperature is above 70°F, you can be sure mold is starting to germinate.

From this information, we can deduce that mold starts to germinate when the relative humidity and temperature are high.

This doesn’t mean you should ignore the dew point. It is also important, especially for your comfort. If you are going out, check the dew point prediction for the day.

Can mold grow in 45 humidity

In various places in this blog, we have said that you should keep the humidity level in your house between 30 and 55%.

In the winter, you can increase this slightly and keep the humidity level between 40 and 60% because then, the air is colder and drier.


  • The correct humidity level for your house is 30 to 50% in summer
  • 30 to 55% humidity level is still comfortable
  • 40 to 60% humidity level is okay-ish but only recommended for winter
  • Above 60%, mold starts to grow in your house, depending on temperature and dewpoint

So, back to the question of whether this fungus will grow at a 45% humidity level, the answer is, no, it will not grow.

Even if the temperature and the dewpoint temperature is high, it is not going to grow. The air moisture content is too low for this fungus to thrive.

45% humidity is perfect for leather items in your house. It is also good for your electronic appliances. It is also quite comfortable for your skin, hair and health.

If the air moisture content goes much lower than this especially in your bedroom, you will experience signs of sleeping in a dry room. And they won’t be good.

How long does it take for mold to grow in high humidity?

How long does it take for mold to grow in high humidity

Back to the numbers we brought you in our mold growth humidity chart, if the relative humidity in your home is 95%, the temperature is 80°F and the dewpoint temperature is 78°F, this fungus will take a maximum of 2 days to grow.

Simply put, in high humidity, meaning above 60%, mold will grow in 2 to 10 days, if the temperature is high.

If the relative humidity is above 60%, and the temperature is between 77 and 86°F, mold will grow. It will also grow in temperatures higher or below the ones given here. The only difference is that it might take longer.

In very low temperatures, say below freezing point, mold spores can die. However, higher than that but still cold, the fungus will just go dormant and wait for the perfect conditions to start thriving again.

To be safe in your home, keep the humidity levels between 30 and 50%. This is also a good humidity level for your bedroom.

This microscopic fungus needs warmth, moisture and nutrients to grow. Therefore, if the humidity level in your house is high, there is wood, paper or other material derived from living things, the fungus will start growing.

Sometimes, it will not grow in the most obvious places where you can see it immediately. That’s why you need to check your crawl spaces.

If you live in a high humidity area, you probably need a basement dehumidifier for mould. You can be sure it (mold) is going to germinate.


A mold growth humidity chart can help you know when to turn on the dehumidifier to lower the moisture level in the air.

Better yet, it helps you interpret the numbers displayed on your hygrometer or humidistat. If the dewpoint temperature is high, it will be a very uncomfortable day.

If the relative humidity level is high in your basement, you need to run a dehumidifier with a drain hose to remove the extra moisture.

When you know under what conditions mold will thrive, you can know when to lower the temperature, run a dehumidifier to lower air moisture level or just let things be.

Remember, mold can survive a long time, staying dormant when the conditions are not right. It is best to remove the infestation from the source to rid your home of this nasty indoor allergen.

Please also check my past posts on:

Air purifier or dehumidifier for musty smell

Can mold cause sinus infection

Is Air Purifier Good For Mold?

Can Mold Grow At 60 Percent Humidity?

Can A Humidifier Cause Mold In Room?

Toxic Black Mold Vs Black Mold