Dew Point Calculator
Enter the air temperature and relative humidity to get the exact dew point — the temperature at which moisture starts to condense — plus wet-bulb, comfort level, and condensation risk.
How to use this dew point calculator
In the calculator above, set Calculate to “Dew Point (I know air temp + humidity)”, choose °F or °C, and enter your two readings. You'll instantly get the dew point along with the dew point depression (how far the air must cool before condensation forms), the wet-bulb temperature, absolute humidity, and a plain-English comfort rating.
What is the dew point?
The dew point is the temperature to which air must be cooled for it to become fully saturated. Unlike relative humidity — which swings up and down as the air heats and cools — the dew point stays fixed unless moisture is physically added or removed from the air. That is exactly why meteorologists treat it as the truest measure of how “muggy” it really feels outside. A 90°F day at a 75°F dew point is miserable; the same 90°F at a 45°F dew point is a dry, pleasant heat.
How the dew point is calculated
This tool uses the Magnus-Tetens formula with the Alduchov & Eskridge (1996) coefficients — the same relationship NOAA relies on. It computes the saturation vapor pressure at your air temperature, scales it by your relative humidity to find the actual vapor pressure, then inverts the equation to solve for the dew point:
e_s(T) = 6.112 × exp(17.625 × T / (243.04 + T)) e = e_s(T) × (RH / 100) Dp = 243.04 × ln(e / 6.112) / (17.625 − ln(e / 6.112))
Dew point comfort scale
| Dew point | How it feels | Notes |
|---|---|---|
| Below 50°F | Dry & pleasant | Crisp air; static and dry skin possible indoors |
| 50–60°F | Comfortable | The ideal range for most people |
| 60–65°F | Getting sticky | Noticeably humid; sweat evaporates slowly |
| 65–70°F | Humid & uncomfortable | Muggy; poor sleep and heat stress begin |
| 70°F and above | Oppressive | Tropical; feels heavy and draining |
Worked example
Say it's 86°F with 60% relative humidity. The saturation vapor pressure at 30°C is about 42.4 hPa; at 60% humidity the actual vapor pressure is roughly 25.5 hPa. Inverting Magnus gives a dew point of about 70°F — right at the “oppressive” threshold, which is why that combination feels so heavy. Prefer to skip the arithmetic? That is exactly what the calculator above is for.
Want the theory? Read Dew Point vs Relative Humidity: Which One Actually Matters? and Condensation Risk: Why Pipes Sweat and How to Stop It. For a full look-up table, see the dew point chart.
Frequently Asked Questions
- What is the dew point?
- The dew point is the temperature air must be cooled to, at constant pressure, before water vapor condenses into liquid. At the dew point the air is fully saturated — 100% relative humidity — and dew, fog, or condensation begins to form.
- How do you calculate dew point from temperature and humidity?
- Multiply the saturation vapor pressure at the air temperature by the relative humidity to get the actual vapor pressure, then invert the Magnus-Tetens equation to solve for the dew point. This calculator does it automatically using the NOAA-standard Alduchov & Eskridge coefficients, accurate to within ±0.35°C.
- What is a comfortable dew point?
- Most people feel comfortable when the dew point is below 60°F (16°C). Between 60 and 65°F the air starts to feel sticky, and above 70°F it feels oppressive and tropical regardless of the actual air temperature.
- Can the dew point be higher than the air temperature?
- No. The dew point can equal the air temperature — that is 100% relative humidity, when fog or dew forms — but it can never exceed it. If a calculation returns a dew point above the air temperature, one of the inputs is wrong.
- What is dew point depression?
- Dew point depression is the gap between the air temperature and the dew point. A small depression means the air is close to saturation. When any surface (a window, a cold pipe, a glass of iced tea) cools below the dew point, moisture condenses on it.