Dew Point Calculator
Find the dew point in °C and °F from air temperature and relative humidity using the Magnus formula.
Dew point
16.68 °C
62.03 °F
Dew point is the temperature at which air becomes saturated and moisture condenses. When it is close to the air temperature, expect fog, dew or rain. Above about 20 °C the air feels sticky.
Last updated: January 2026
How this calculator is verified
Checked by True Calculator automated test suite on
- Formula verified against a published worked example in the automated test suite
- Edge cases (zero, negative, boundary and unit-mismatch inputs) covered by unit tests
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When to Use This Calculator
Use this calculator when checking how close the air is to condensation: before deciding whether to dry clothes outdoors, when storing hygroscopic goods like cement, flour or seeds that spoil in damp air, or when planning a trek where fog can settle in valleys. Painters use it to decide if a surface will sweat before the coating cures; farmers use it to judge when a wet crop will dry. In India the dew point explains why monsoon nights feel heavy even when the temperature is moderate, and why air conditioners drip water. It is also the number behind 'dew on the grass in the morning' — the ground cools to the dew point overnight. Enter your local readings and you will understand the humidity of any place or season instantly.
How to Use This Calculator
- Step 1: Note the current air temperature in °C from a thermometer or weather app.
- Step 2: Note the relative humidity percentage for the same time and place.
- Step 3: Enter both values — the dew point is computed with the Magnus formula.
- Step 4: Compare the dew point with the air temperature to judge how close the air is to saturation.
Worked Example
At 30 °C with 70% relative humidity, the dew point is 23.92 °C. That is within 6 °C of the air temperature, meaning the air is quite moist — typical of a humid Indian evening before rain. At 25 °C and 60% humidity the dew point drops to 16.68 °C, which feels drier and more comfortable. The closer the two numbers, the more likely fog, dew or drizzle.
Tips and Common Mistakes
- •Tip 1: A dew point within 3 °C of air temperature means near-saturation — expect condensation.
- •Tip 2: Dew point above 20 °C feels muggy; above 24 °C is oppressive even at night.
- •Tip 3: Measure humidity at the same spot as the temperature — a sunny wall shifts both readings.
- ✗Mistake 1: Do not confuse dew point with relative humidity — 60% humidity can feel dry or sticky depending on temperature.
- ✗Mistake 2: Do not use the dew point to predict rain by itself; cloud cover and wind matter as much.
Frequently Asked Questions
What is the dew point?
The dew point is the temperature at which air becomes fully saturated and moisture condenses. At 25 °C and 60% relative humidity the dew point is about 16.7 °C — below that temperature, dew or fog forms.
How is dew point calculated?
This calculator uses the Magnus formula: dew point = 243.5 × γ ÷ (17.62 − γ), where γ = ln(RH/100) + 17.62 × T ÷ (243.5 + T). You only need temperature and relative humidity as inputs.
What does a high dew point mean?
A dew point above 20 °C feels muggy and sticky; above 24 °C is uncomfortable for most people. A dew point close to the air temperature means near-100% humidity, with fog, dew or rain likely.
What is the difference between dew point and relative humidity?
Relative humidity is a percentage that changes with temperature; dew point is an absolute measure of moisture. A dew point of 20 °C always means the same amount of water vapour, whatever the temperature.
Why is the dew point important in India?
Monsoon months push dew points above 24 °C in much of the country, making nights feel oppressive. Knowing the dew point helps plan drying times, storage of hygroscopic goods and comfort expectations.
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