Financial term · Reviewed August 17, 2026
Dew point
Dew point: The temperature air would need to cool to for it to become fully saturated with the moisture it currently holds. A higher dew point means more humid, muggier air. The Dew Point Calculator returns this figure from magnus formula on temperature (°f) and relative humidity (%). At that calculator’s documented worked-example inputs the dew point (°f) is 57.7; holding every other input steady, moving air temperature (°f) from 60 to 90 moves it from 43.8 to 71.6, a spread of 27.8.
Relative humidity is relative to temperature, which makes it nearly useless for comparing two days. Sixty percent on a cold morning and sixty percent on a hot afternoon are not remotely the same air. Dew point describes how much moisture is actually there, in absolute terms. So it can be compared directly. Above about sixty-five it starts feeling sticky to most people and above seventy it is oppressive, regardless of what the humidity percentage says.
| Term | Dew point |
|---|---|
| Category | Weather |
| How it is found | Magnus formula on temperature (°F) and relative humidity (%) |
| Worked example | Dew point (°F): 57.7 |
| Computed by | Dew Point Calculator |
| Related terms | 1 defined in this glossary |
Before you rely on it
What to check
Compare dew points, not humidity percentages, when judging comfort or condensation risk.
The common error
Where people go wrong with dew point
Sizing a dehumidifier or diagnosing window condensation from relative humidity alone. The absolute moisture load is what determines whether water forms on a cold surface.
Worked through
Dew point in plain numbers
Air at 30°C with 60% relative humidity has a dew point of about 21.4°C. That means if the air cooled to 21.4°C at constant moisture, it would be saturated, and dew would begin to form. Now take 30°C at 30% humidity. The dew point is about 10.5°C, and the same warm day feels much drier; many people find dew points above roughly 20°C (68°F) muggy and dew points below about 10°C (50°F) comfortable. The dew point tells you how much water vapor is actually in the air, while relative humidity depends on the temperature.
Easily confused
Dew point and its neighbours
Dew point is not relative humidity. Relative humidity says how close the air is to saturation at its current temperature, so it swings through the day as temperature changes even when the moisture stays the same. The dew point measures actual moisture and changes only when moisture is added or removed, and it is also different from the heat index and wet-bulb temperature, which combine heat and humidity to describe stress on the body. For judging how muggy it feels, the dew point is usually the clearer number.
In real decisions
Where dew point turns up
Forecasters use it to predict fog, frost and dew. Farmers watch it for frost risk and disease pressure. HVAC engineers use it to avoid condensation in ducts and walls. Builders and homeowners look at it to manage basement moisture. Pilots use the gap between temperature and dew point to estimate cloud base. Runners use it to gauge comfort. When the temperature falls to the dew point overnight, expect fog or dew.
Know the edges
Where dew point stops being reliable
Formulas such as Magnus give good estimates within ordinary ranges and drift at extremes. Sensors have errors, especially at high humidity. Local conditions, wind and surfaces alter whether dew forms. Comfort thresholds vary between people. The figure describes air near the sensor and not the whole atmosphere, and treat a calculator result as an estimate, and use official forecasts for safety decisions.
Quick answers
What people ask about dew point
Why does fog form when temperature falls to the dew point? At that temperature the air is saturated, so extra cooling makes water vapor condense into tiny droplets. Fog is a cloud at ground level.
What dew point feels comfortable? Many people feel comfortable below about 60°F (16°C) and find levels above 70°F (21°C) oppressive. Preferences differ.
Put it to work
How dew point is calculated
At the dew point calculator’s worked-example inputs, dew point (°f) is 57.7, temperature-dew point spread is 17.3. Moving air temperature (°f) from 60 to 90 moves that first figure from 43.8 to 71.6.
Open the Dew Point Calculator →
Wind chill and heat index use National Weather Service formulas, most accurate within their documented valid ranges (wind chill: 50°F or below with wind at or above 3 mph). Extreme inputs outside those ranges are not meteorologically meaningful.
Keep reading
Nearby in the glossary
- ← Determinant
- Discount rate →
- All 174 defined termsThe complete Free Calculators Online financial glossary.