Unit of Humidity - Relative Humidity, Absolute Humidity & Specific Humidity

Edited By Vishal kumar | Updated on Jul 02, 2025 05:04 PM IST

Introduction
In this chapter, we will study humidity and its units. Further we will study Relative and absolute humidity and see the difference between relative and absolute humidity. In this chapter, we will study about humidity measurement.
NOTE: Meaning of humidity in Telugu/humidity meaning in telugu is తేమ
Meaning of humidity in Tamil/humidity meaning in tamil is ஈரப்பதம்

This Story also Contains

What is Humidity?
Types of humidity
Difference between Absolute humidity and relative humidity

Unit of Humidity - Relative Humidity, Absolute Humidity & Specific Humidity

What is Humidity?

Humidity is a scientific term, which means concentration of water vapor present in air. Humidity at any place is dependent on pressure and temperature. It can be stated as, saturation point of holding water vapor increases as temperature increases.

Also read -

Types of humidity

Generally, we talk about three types of humidity namely,

Absolute humidity
Relative humidity
Specific humidity

What is absolute humidity?

Absolute humidity is defined as the total mass of water vapor present per unit volume of air. It does not take air into consideration. It is highly variable as it is dependent on temperature and pressure, so this way of measuring humidity does not fit in Chemical Engineering. It is given by the numerical formula:

$AH=\frac{m_h_2{^0}}{v_{net}}$

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What is meant by relative humidity?

The relative humidity is defined as the total mass of water vapor present in per unit volume of air but the difference lies in dependency on air. It takes air in consideration. It is a measure of water vapor in the air as the total percentage it could hold at specific temperature.

Also Read: NCERT Solutions for Class 6 Physics Chapter 15 Air Around Us

Difference between Absolute humidity and relative humidity

Apart from taking temperature into consideration there are few basic differences between them.
Absolute humidity is expressed in grams per cubic meter while Relative humidity is expressed in percentage.
As Absolute humidity does not take air into consideration, it is not so accurate compared to relative humidity. Relative humidity gives a fair idea of humidity at a particular temperature.

In this way we can distinguish between absolute humidity and relative humidity.

Dew point Temperature

Dew point is the temperature at which water vapor at constant pressure condenses into liquid water at the same rate at which it evaporates.

When temperature is lower than dew point then rate of condensation is greater than evaporation. The condensed liquid is called dew when condensed on the surface.

Also check-

NCERT Physics Notes:

Frequently Asked Questions (FAQs)

1. During which part of the year, it is most likely to form dew?

As we have read about Dew point, Dew forms on the surface when temperature cools down to the dew point. Formation of dew happens when dew point is below the freezing point, so generally dew is most likely to form during winter days.

2. What it means when it is said- Relative humidity is 100% saturated.

Relative density is the ratio between water vapor present in a given volume of air compared to water vapor present at a saturated level at given pressure and temperature, so when the ratio comes to be 1 then it means Relative humidity is 100% saturated.

3. What measures humidity in the air?/air humidity measurement is done by which instrument?

Hygrometer used to measure humidity in the air.

4. Write the humidity symbol

RH(relative humidity) is the humidity symbol.

5. What's the difference between relative humidity and absolute humidity?

Relative humidity is the amount of water vapor in the air compared to the maximum amount the air can hold at that temperature, expressed as a percentage. Absolute humidity is the actual amount of water vapor in a given volume of air, typically measured in grams per cubic meter. Relative humidity changes with temperature, while absolute humidity does not.

6. Why does relative humidity change when temperature changes, even if the amount of water vapor stays the same?

Relative humidity changes with temperature because warm air can hold more water vapor than cold air. As air warms, its capacity to hold water vapor increases, so the relative humidity decreases if no more moisture is added. Conversely, as air cools, its capacity decreases, causing relative humidity to increase.

7. What is specific humidity and how does it differ from absolute humidity?

Specific humidity is the ratio of water vapor mass to the total mass of the air parcel, usually expressed in grams of water vapor per kilogram of air. Absolute humidity is the mass of water vapor per unit volume of air. While they both measure actual water vapor content, specific humidity uses mass ratios while absolute humidity uses volume.

8. Why do we often use relative humidity instead of absolute or specific humidity in weather reports?

Relative humidity is commonly used in weather reports because it directly relates to how humans perceive moisture in the air. It gives us a sense of how close the air is to saturation, which affects our comfort and the likelihood of precipitation. Absolute or specific humidity doesn't provide this context about the air's moisture-holding capacity.

9. How does a hygrometer measure relative humidity?

A hygrometer measures relative humidity by using materials that change in response to moisture. Common types include:

10. What is the dew point, and how is it related to humidity?

The dew point is the temperature at which air becomes saturated and water vapor begins to condense into liquid water. It's directly related to the amount of water vapor in the air (absolute humidity). When the air temperature equals the dew point, the relative humidity is 100%.

11. What is the relationship between humidity and cloud formation?

Clouds form when water vapor in the air condenses into liquid water droplets or ice crystals. This occurs when the relative humidity reaches 100% (saturation) and the air cools to its dew point. Higher humidity levels increase the likelihood of cloud formation as less cooling is required to reach saturation.

12. How does humidity affect the human body's ability to cool itself?

High humidity reduces the effectiveness of sweating, our body's primary cooling mechanism. Sweat evaporates more slowly in humid conditions, making it harder for the body to release heat. This is why a hot, humid day feels more uncomfortable than a hot, dry day at the same temperature.

13. Why does wood expand in humid conditions?

Wood expands in humid conditions because it's hygroscopic, meaning it can absorb moisture from the air. As the relative humidity increases, wood fibers absorb water molecules, causing them to swell. This property is why wooden doors might stick in summer and why wooden furniture can warp in damp environments.

14. How does humidity affect the rate of evaporation?

Humidity inversely affects the rate of evaporation. Higher humidity means there's more water vapor in the air, which reduces the air's capacity to accept more water vapor. This slows down evaporation. Conversely, lower humidity accelerates evaporation as the air can more readily accept water vapor.

15. What is humidity and why is it important to measure?

Humidity is the amount of water vapor present in the air. It's important to measure because it affects our comfort, influences weather patterns, and impacts various industrial processes. Understanding humidity helps us predict weather, manage indoor environments, and optimize many manufacturing processes.

16. What is "muggy" weather in terms of humidity?

"Muggy" weather refers to hot and humid conditions that feel uncomfortable. It typically occurs when temperatures are high (usually above 70°F or 21°C) and relative humidity is above 60%. The high moisture content in the air makes it feel sticky and oppressive, as it hinders the body's ability to cool through sweating.

17. How does humidity affect the formation of fog?

Fog forms when water vapor in the air condenses into tiny water droplets suspended in the atmosphere. High humidity is crucial for fog formation because it means the air is close to its saturation point. When the air cools to its dew point (often due to contact with a cold surface or radiative cooling at night), fog can form if there are sufficient condensation nuclei present.

18. How does humidity affect the perceived temperature in cold weather?

In cold weather, humidity can make it feel colder than the actual temperature. This is because moist air conducts heat away from the body more efficiently than dry air. Additionally, when moisture from humid air condenses on the skin, it can create a chilling effect, similar to how sweat cools us in warm weather.

19. How does humidity affect the efficiency of cooling towers in industrial settings?

Humidity significantly impacts cooling tower efficiency:

20. What is the relationship between humidity and atmospheric pressure?

Humidity and atmospheric pressure are inversely related. As humidity increases, the density of air decreases because water vapor (H2O) is less dense than dry air (primarily N2 and O2). This decrease in density leads to a slight decrease in atmospheric pressure. However, this effect is usually small compared to other factors affecting pressure, like temperature and altitude.

21. How does humidity affect the performance of electrostatic devices?

Humidity can significantly impact electrostatic devices:

22. How does humidity affect the accuracy of ballistic calculations in shooting sports?

Humidity affects ballistic calculations in several ways:

23. How does humidity affect the perceived loudness of sound?

Humidity can affect the perceived loudness of sound:

24. How does humidity affect the efficiency of solar panels?

Humidity can impact solar panel efficiency in several ways:

25. How does humidity affect the perception of odors?

Humidity can influence odor perception in several ways:

26. What is the relationship between humidity and the formation of mirages?

While mirages are primarily caused by temperature gradients in the air, humidity can play a role:

27. How does humidity affect the performance of wind instruments?

Humidity significantly impacts wind instruments:

28. How does humidity affect the process of sublimation?

Humidity influences sublimation, the process where a solid changes directly to a gas without passing through the liquid phase:

29. What is the relationship between humidity and the formation of halos around the sun or moon?

Humidity plays an indirect role in halo formation:

30. How does humidity affect the efficiency of dust collection systems?

Humidity can significantly impact dust collection efficiency:

31. Can relative humidity ever exceed 100%?

In theory, relative humidity cannot exceed 100% because it represents the percentage of the air's water vapor holding capacity. However, in practice, air can become supersaturated under certain conditions, leading to readings slightly above 100%. This unstable state quickly results in condensation or fog formation.

32. How does humidity affect the spread of airborne diseases?

Humidity can influence the spread of airborne diseases in several ways:

33. How does humidity affect the performance of air conditioning systems?

Humidity significantly impacts air conditioning performance:

34. What is the "heat index" and how is it related to humidity?

The heat index, also known as the "feels like" temperature, combines air temperature and relative humidity to determine how hot it actually feels to the human body. High humidity makes it feel hotter than the actual air temperature because it reduces the body's ability to cool through sweating.

35. Why do some climates have higher average humidity than others?

Climate humidity variations are influenced by several factors:

36. What is the concept of "mixing ratio" in relation to humidity?

The mixing ratio is the mass of water vapor per unit mass of dry air, typically expressed in grams of water vapor per kilogram of dry air. It's a measure of humidity that, unlike relative humidity, doesn't change with temperature if no water vapor is added or removed. The mixing ratio is useful in meteorology for tracking air masses and understanding atmospheric processes.

37. Why do hair and fur become frizzy in humid conditions?

Hair and fur become frizzy in humid conditions because they are hygroscopic, meaning they absorb moisture from the air. As hair fibers absorb water molecules, they swell and can change shape, leading to frizz. Additionally, high humidity can break the hydrogen bonds within hair strands, allowing them to reposition and create a frizzy appearance.

38. What is the role of humidity in the water cycle?

Humidity plays a crucial role in the water cycle:

39. What is the relationship between humidity and the formation of rainbows?

Humidity is indirectly related to rainbow formation:

40. What is the concept of "partial pressure" in relation to humidity?

Partial pressure is a key concept in understanding humidity:

41. What is the concept of "vapor pressure deficit" and how is it related to humidity?

Vapor pressure deficit (VPD) is the difference between the amount of moisture in the air and how much moisture the air can hold when saturated:

42. What is the concept of "wet-bulb temperature" and how is it related to humidity?

Wet-bulb temperature is the lowest temperature that can be achieved by evaporative cooling:

43. How does humidity affect the process of food dehydration?

Humidity significantly impacts food dehydration: