The temperature at which air becomes saturated and moisture starts to condense. Higher dew points mean more humid, oppressive conditions.
measurementWhat is Dew Point?
The dew point is the temperature to which air must be cooled — at constant pressure and water-vapour content — for water vapour to condense into liquid water (dew, fog, or cloud droplets). It is a direct measure of how much moisture the air actually contains.
Unlike relative humidity, dew point does not depend on the current air temperature. A dew point of 24°C means the air contains a fixed amount of water vapour regardless of whether the thermometer reads 28°C or 38°C. This makes dew point the best single indicator of “how muggy it feels.”
When the air temperature drops to the dew point, relative humidity reaches 100% and condensation begins. This is why mornings often start with fog or dew on grass — the overnight air cooled to its dew point.
Why dew point beats relative humidity for comfort
Relative humidity is confusing because it depends on temperature. The same air can read “100% RH” at 5 AM and “60% RH” by noon, even though the actual moisture is unchanged — the air simply warmed up.
Dew point gives you a fixed comfort baseline:
| Dew point | What it feels like |
|---|---|
| Below 10°C | Dry, crisp |
| 10–13°C | Comfortable |
| 13–16°C | Pleasant, slight humidity |
| 16–18°C | Noticeable humidity |
| 18–21°C | Sticky, uncomfortable for many people |
| 21–24°C | Oppressive, heavy air |
| 24–26°C | Severe — most people sweat constantly |
| Above 26°C | Dangerous — heat-stress risk |
For comparison, Delhi’s dew point in May is often only 8–12°C (dry heat). But during monsoon in July–August, Delhi dew point can hit 26°C, and Mumbai or Kolkata routinely sees 25–28°C — among the highest in the world.
Dew point in South Asia
South Asia has some of the highest dew points on Earth during the monsoon:
- Coastal cities (Mumbai, Chennai, Karachi, Dhaka, Chittagong, Kochi): dew point 24–28°C through summer and monsoon.
- Indo-Gangetic plain in July–September: dew point 24–27°C.
- Northwest India and interior Pakistan in May–June: dew point only 8–15°C — dry heat that feels less oppressive despite higher temperatures.
- Bangladesh delta: dew point above 26°C in much of the monsoon.
This is why “feels-like” temperature reads dramatically higher in coastal South Asia. A 32°C day with a 27°C dew point feels far more dangerous than a 42°C day with a 12°C dew point.
Dew point and dangerous heat
Climate scientists are increasingly worried about wet-bulb temperature, which is closely related to dew point. When wet-bulb temperature reaches 35°C, the human body cannot cool itself via sweating, and even healthy adults face heatstroke within hours.
Several South Asian coastal locations have already recorded wet-bulb readings approaching this threshold:
- Jacobabad, Pakistan: 35°C wet-bulb in 2020 (one of the highest ever measured)
- Ras al Khaimah, UAE: similar levels
- Bay of Bengal coast: increasingly frequent 32–33°C wet-bulb events
A 30°C dew point on a 35°C day is approaching survivability limits. This is why coastal heat is now considered more dangerous than the dry desert heat of inland Rajasthan.
How dew point is used
- Pilots use dew point to predict fog and icing.
- Air-conditioning engineers size systems based on dew point, not just temperature.
- Greenhouse and warehouse operators monitor dew point to prevent condensation damage.
- Meteorologists use the temperature-dew point spread to forecast cloud formation and rain.
- Athletes and outdoor workers check dew point as a heat-stress indicator.
Frequently asked questions
What is a “high” dew point? Anything above 18°C feels humid; above 21°C is oppressive; above 24°C is severe. Dew points above 26°C — common in coastal South Asia during monsoon — make outdoor exertion dangerous.
How is dew point different from humidity? Relative humidity changes with temperature; dew point doesn’t. A dew point of 22°C means the same moisture content whether the air is 25°C or 40°C. RH would read 80% at the cooler temperature and 30% at the hotter one — different numbers for the same air.
Can dew point be higher than the air temperature? No. By definition, dew point cannot exceed the current temperature. If they are equal, RH = 100% and condensation occurs.
Why does Mumbai feel worse than Delhi in summer? Mumbai dew point in May is around 25°C; Delhi is around 12–15°C. Even at the same air temperature, Mumbai feels far more oppressive because the air is already loaded with moisture.
Where can I see dew point for my city? The Mausam Online “feels-like” temperature combines dew-point and wind chill into a single comfort metric. Live readings are available on every city page: Mumbai, Kolkata, Karachi, Dhaka.