Dew Point Calculator
Find the exact temperature at which air becomes saturated. Essential for HVAC, gardening, meteorology, and comfort assessment.
Dew Point
52.3
°F
Comfort Level
Pleasant
Heat Index (≥80°F & ≥40% RH)
—
Feels Like (humidity-adjusted)
Dew Point vs. Relative Humidity: What's the Difference?
Relative Humidity tells you how saturated the air is at its current temperature — but the same 60% RH can feel completely different on a hot day versus a cold one. The dew point is an absolute measure: it tells you exactly how much water vapour is in the air, regardless of temperature.
Meteorologists and HVAC engineers prefer the dew point because it never lies. A dew point of 70°F (21°C) is oppressive whether the thermometer reads 75°F or 95°F.
The Magnus-Tetens Formula
This calculator uses the industry-standard Magnus-Tetens approximation (a = 17.625, b = 243.04°C), accurate to within ±0.4°C for temperatures between −45°C and 60°C. The formula computes the intermediate value α from your inputs, then derives the dew point directly.
Frost Point
When the calculated dew point falls below 0°C (32°F), it becomes the frost point — the temperature at which water vapour deposits directly as ice crystals rather than liquid dew. Gardeners use this to predict overnight frost events.
Comfort Scale
Below 50°F (10°C): dry and crisp. 50–60°F: comfortable. 60–65°F: starting to feel sticky. 65–70°F: noticeably humid and uncomfortable. Above 70°F: oppressive — the body struggles to cool itself through perspiration.
Heat Index
When the air temperature is 80°F+ and RH is 40%+, the NWS Heat Index formula calculates how hot it actually feels. High dew points dramatically amplify the apparent temperature because sweat evaporates more slowly in moist air.
When Does Dew Form?
Dew forms on surfaces when their temperature drops to or below the dew point of the surrounding air. Clear nights allow surfaces to radiate heat into space, cooling rapidly. If a surface — grass, a car roof, a window — cools to the dew point, water condenses on it. The higher the dew point, the more dew will form and the less cooling is required.
Frequently Asked Questions
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