Weather Calculator

Dew Point Calculator

Enter the air temperature and relative humidity to get the dew point in °F or °C, or switch modes to find relative humidity from a dew point. The dew point is the temperature air has to cool to before it becomes saturated, and it's the most direct gauge of how humid it feels: under 60°F (16°C) is comfortable for most people, and above 65°F (18°C) starts to feel sticky.

Air Temperature (°F)

Relative Humidity (%)

Dew Point

62.4°F

16.9°C

Somewhat Humid

Slightly muggy. Some people begin to feel the humidity at this level.

Dew Point Formula

This calculator uses the Magnus-Tetens approximation, a standard formula that is reliable for temperatures between -40°C and 50°C. Work in Celsius, with relative humidity (RH) as a percentage:

Dew point from temperature and humidity

γ = ln(RH / 100) + 17.27 × T / (237.7 + T)

Td = 237.7 × γ / (17.27 - γ)

Relative humidity from dew point

RH = 100 × e^(17.27 × Td / (237.7 + Td) - 17.27 × T / (237.7 + T))

Worked example: at 75°F (23.9°C) and 65% relative humidity, γ = 1.146, so the dew point is 16.9°C, or 62.4°F.

Quick estimate: in Celsius, dew point ≈ T - (100 - RH) / 5. Between 5°C and 35°C (41°F to 95°F) with relative humidity above 60%, it lands within about 1°C of the full formula. It drifts further off in colder or drier air.

The dew point can never exceed the air temperature. When the two are equal, relative humidity is 100% and fog or dew is likely to form.

Dew Point Chart by Temperature and Humidity

Dew point in °F, rounded to the nearest degree. Find the air temperature on the left and the relative humidity across the top. Use the °F / °C switch above to change units.

Dew point in °F for air temperatures from 40°F to 100°F and relative humidity from 30% to 90%
Temp	30%	40%	50%	60%	70%	80%	90%
40°F	11	18	23	27	31	34	37
50°F	20	27	32	37	41	44	47
60°F	28	36	41	46	50	54	57
70°F	37	45	50	55	60	64	67
80°F	46	53	60	65	69	73	77
90°F	54	62	69	74	79	83	87
100°F	63	71	78	84	88	93	97

Dew Point Comfort Levels

Dry

Below 50°F

Below 10°C

Very comfortable. Air feels dry and pleasant for all activities.

Comfortable

50-60°F

10-16°C

Pleasant conditions. Most people find this ideal.

Somewhat Humid

60-65°F

16-18°C

Slightly muggy. Some sensitivity to humidity begins.

Humid

65-70°F

18-21°C

Uncomfortable for most. You'll notice the humidity.

Very Humid

70-75°F

21-24°C

Oppressive. Sweating becomes less effective for cooling.

Extremely Humid

75°F+

24°C+

Dangerous. High risk of heat-related illness.

Understanding Dew Point

What is Dew Point?

The dew point is the temperature at which air becomes saturated with water vapor and dew begins to form. It's an absolute measure of moisture in the air, unlike relative humidity which changes with temperature.

Why Dew Point Matters

Dew point is the best indicator of comfort because it directly measures how much moisture is in the air. High dew points make it harder for sweat to evaporate, making you feel hotter and more uncomfortable.

Dew Point vs. Humidity

Relative humidity can be misleading: 50% humidity at 90°F feels much worse than 50% at 60°F. Dew point gives a consistent measure: a 70°F dew point always feels oppressive, regardless of the actual temperature.

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Frequently Asked Questions

How do you calculate dew point from temperature and humidity?

Convert the temperature to Celsius, then use the Magnus formula: γ = ln(RH/100) + 17.27 × T / (237.7 + T), and dew point = 237.7 × γ / (17.27 - γ). For example, 75°F (23.9°C) at 65% relative humidity gives a dew point of about 62°F (17°C). A quick shortcut in Celsius is dew point ≈ T - (100 - RH) / 5, which stays within about 1°C between 5°C and 35°C when humidity is above 60%, and drifts further off in colder or drier air.

How do you find relative humidity from the dew point?

With both values in Celsius, relative humidity = 100 × e^(17.27 × Td / (237.7 + Td) - 17.27 × T / (237.7 + T)). Switch this calculator to Find Relative Humidity and enter the air temperature and dew point to do it automatically. An 80°F afternoon with a 60°F dew point works out to about 50% relative humidity.

What is a comfortable dew point?

Most people find a dew point between 50°F and 60°F (10°C to 16°C) comfortable. From 60°F to 65°F (16°C to 18°C) the air starts to feel muggy, 65°F to 70°F (18°C to 21°C) feels sticky, and above 70°F (21°C) feels oppressive because sweat evaporates slowly. Below 50°F (10°C) the air feels dry.

Can the dew point be higher than the air temperature?

Not in ordinary conditions. The dew point can equal the air temperature, which means relative humidity is 100% and the air is saturated, so fog, dew, or frost can form. If the air keeps cooling, water vapor condenses out and the dew point falls along with the temperature.

Why is dew point a better measure of humidity than relative humidity?

Relative humidity depends on temperature, so the same air can read 90% at dawn and under 50% in the afternoon without any moisture coming or going. The dew point stays roughly steady as the temperature changes, so it tracks the actual amount of water vapor in the air and how muggy it will feel.

What does the dew point tell you about fog and frost?

When the air cools to its dew point, it is saturated and water starts to condense. On calm, clear nights, a small gap between the evening temperature and the dew point is a sign that fog or dew may form by morning. When the dew point is below freezing, the same process can leave frost instead.