💧Dew Point Calculator
Calculate dew point temperature from air temperature and relative humidity, or find relative humidity from temperature and dew point, or find air temperature from humidity and dew point. Also shows absolute humidity, heat index, and comfort level.
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Result
13.22 °C
Temperature and Dew Point (°C)
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Dew Point Calculator: Temperature, Humidity, and Dew Point Explained
The dew point is the temperature to which air must be cooled to become saturated with water vapor. When air temperature equals dew point, relative humidity = 100% and dew forms. At 20°C and 65% RH, the dew point is approximately 13.2°C. A dew point above 21°C feels oppressively humid; below 10°C feels dry and comfortable.
Formula: Td = β × γ / (α − γ) where γ = ln(RH/100) + α×T/(β+T), α=17.625, β=243.04
| Dew Point | Comfort Level | Description |
|---|---|---|
| Below 10°C (50°F) | ✅ Dry | Very comfortable, desert-like |
| 15–18°C (59–64°F) | 🟡 Slightly humid | Typical comfortable summer day |
| Above 24°C (75°F) | 🔴 Oppressive | Tropical, dangerous in heat |
Meteorologists and HVAC engineers use dew point — rather than relative humidity — as a more absolute measure of atmospheric moisture. Relative humidity changes as temperature changes even when the actual moisture content stays the same. Dew point stays constant when moisture content is unchanged, making it a better indicator of comfort and condensation risk.
Why Dew Point Is Better Than Relative Humidity for Comfort
Relative humidity (RH) is the ratio of current vapor pressure to saturation vapor pressure at the current temperature. The same RH can feel very different depending on temperature: 65% RH at 15°C is pleasant; 65% RH at 35°C is brutally uncomfortable. Dew point is an absolute measure — it directly represents how much water vapor is in the air. A dew point of 21°C always feels muggy, regardless of air temperature. This is why weather forecasters in humid regions increasingly report dew point instead of or alongside relative humidity.
Frequently Asked Questions
What is the dew point temperature?
The dew point is the temperature at which air must be cooled (at constant pressure and water content) to become saturated — that is, to reach 100% relative humidity. When air cools to the dew point, water vapor condenses on surfaces as dew. When the dew point is below 0°C, frost forms instead. The dew point is an absolute measure of atmospheric moisture: higher dew point = more water vapor in the air. Dew point and air temperature are equal only at 100% relative humidity (fog, rain, or saturated conditions).
What is a comfortable dew point temperature?
Most people find dew points below 15°C (59°F) comfortable. Between 15–18°C (59–64°F) feels slightly humid but acceptable. At 18–21°C (64–70°F), humidity is noticeably uncomfortable. Above 21°C (70°F), conditions feel muggy to oppressive. Above 24°C (75°F) is extremely uncomfortable and potentially dangerous in hot weather because it impairs the body's ability to cool itself through sweat evaporation. The record highest dew points (around 35°C / 95°F) occur in the Persian Gulf, where conditions are essentially unbreathable.
What is the difference between dew point and relative humidity?
Relative humidity (RH) is a ratio — it depends on both the moisture in the air and the air temperature. The same amount of moisture gives different RH at different temperatures: 10 g of water vapor per kg of air is 49% RH at 20°C but only 21% RH at 30°C. Dew point is absolute — it depends only on the actual moisture content, not temperature. For comfort, dew point is more meaningful: a 25°C dew point always feels oppressive regardless of air temperature. RH of 50% can feel comfortable or oppressive depending on air temperature.
What causes condensation on windows and pipes?
Condensation forms when a surface temperature drops to or below the dew point temperature of the surrounding air. Cold windows, pipes, and cans of cold drinks cool the adjacent air below its dew point, causing water vapor to condense on the surface. To prevent condensation: reduce indoor humidity (dehumidifier, ventilation); increase surface temperature (insulation, double-pane windows, pipe insulation); or lower the dew point by reducing moisture sources (cooking lids, exhaust fans in bathrooms). The critical surface temperature threshold is the dew point — keep surfaces above it to prevent condensation.