Calculate dew point from air temperature and relative humidity, estimate relative humidity from temperature and dew point, and understand what dew point says about moisture in the air.
Choose a mode, enter your values, and press Calculate for an instant result.
Find Dew Point: enter air temperature and relative humidity to estimate the dew point.
The dew point is the temperature to which air must be cooled for it to become saturated, assuming pressure and moisture content remain constant. That definition comes from the National Weather Service. At the dew point, relative humidity reaches approximately 100%. If cooling continues, some water vapor can condense into liquid water. This can contribute to dew, fog, or cloud droplets, depending on where and how the condensation occurs.
Cooling air toward its dew point moves it toward saturation. Reaching the dew point does not guarantee precipitation; it means the air has reached its moisture limit at that temperature.
| Stage | What Happens |
|---|---|
| Air Temperature | Starting condition entered into the calculator |
| Cool Air | Temperature drops toward the dew point |
| Dew Point Reached | Air becomes approximately saturated, RH ≈ 100% |
| Saturation | Further cooling can allow condensation such as dew, fog, or cloud droplets |
If you know air temperature and relative humidity, you can estimate the dew point mathematically. CalculateThisWay uses a Magnus-type equation consistent with NOAA/NCEP meteorological calculation methods. The equation works most cleanly when temperature is converted to Celsius first. The calculator handles the logarithms and exponential terms automatically.
| You Know | Mode | Formula Direction |
|---|---|---|
| Temperature + Relative Humidity | Find Dew Point | Solves the Magnus equation for dew point |
| Temperature + Dew Point | Find Relative Humidity | Reverses the same vapor-pressure relationship for RH |
| Temperature + Dew Point | Compare | Shows the spread and an estimated relative humidity |
Dew point is a measure of atmospheric moisture. A higher dew point means more moisture is in the air. A lower dew point means less moisture. Relative humidity is different because it depends strongly on the current air temperature. This is why a 90% relative humidity reading on a cold morning does not necessarily mean the air contains more moisture than 50% relative humidity on a hot summer afternoon.
Relative humidity compares the moisture currently in the air with how much would be required for saturation at the current temperature. Warm air can reach a lower relative humidity while still containing substantial moisture. The National Weather Service gives an example along these lines: cold air at high relative humidity can contain less moisture than much warmer air with a lower RH.
Same amount of moisture in the air: cooler air shows a higher relative humidity, warmer air shows a lower relative humidity, while the dew point itself stays about the same if moisture content is unchanged.
| Condition | Relative Humidity |
|---|---|
| Cooler Air | Higher relative humidity |
| Warmer Air | Lower relative humidity |
| Dew Point | Stays about the same if moisture content is unchanged |
That is why dew point is often easier to interpret when the question is: how much moisture is actually in the air?
Yes. Suppose the moisture content remains nearly constant. If the air warms, relative humidity usually falls. If the air cools, relative humidity usually rises. The dew point may remain relatively stable because the moisture content itself did not change much. This is a major reason morning RH can be high and afternoon RH can be much lower even on the same day.
If air temperature equals dew point, the air is approximately saturated. Relative humidity is approximately 100%. That does not guarantee rain. It simply means the air has reached saturation at that temperature and moisture content.
At the same observation point under ordinary atmospheric conditions, dew point should not exceed the actual air temperature. If a user enters Temperature: 60°F and Dew Point: 70°F, the calculator asks them to check the values rather than generating a normal relative-humidity result. Tiny computational differences caused by rounding are different and can be handled within numerical tolerance.
Dew point depression is air temperature minus dew point. Example: Temperature 80°F, Dew Point 60°F, Difference 20°F.
A small spread generally indicates air closer to saturation. A larger spread means temperature is farther above the dew point.
| Value | Reading |
|---|---|
| Temperature | 80°F |
| Dew Point | 60°F |
| Difference | 20°F |
It can indicate that the air is closer to saturation, but fog is not guaranteed. Fog development also depends on cooling, wind, mixing, terrain, moisture supply, and atmospheric structure. Use the dew point as one piece of information rather than a guaranteed fog prediction.
The National Weather Service Tampa Bay office provides a general summer comfort reference. It describes dew points roughly 55°F or lower as relatively dry/comfortable, 55°F to 65°F as becoming stickier, and 65°F and above as containing a lot of moisture and becoming increasingly oppressive.
General warm-weather comfort reference from the National Weather Service. This describes typical human perception, not a medical threshold, and individual perception varies.
| Dew Point Range | General Reference |
|---|---|
| 55°F or lower | Relatively dry / comfortable |
| 55°F to 65°F | Increasingly sticky |
| 65°F and above | A lot of moisture / increasingly oppressive |
These are general comfort descriptions. They are not medical thresholds. They can also feel different depending on temperature, sun, wind, activity, and personal tolerance.
A dew point around 60°F usually indicates noticeable moisture compared with very dry air. Using the general NWS warm-season comfort framework, it falls in the range where conditions can begin to feel sticky, especially during warm weather. Do not interpret the number without considering actual air temperature.
A dew point around 70°F means there is substantial atmospheric moisture. Warm weather with dew points in this range often feels muggy. However, dew point alone does not determine heat danger. For heat safety, use official Heat Index, HeatRisk, and NWS warnings.
Yes, particularly in very humid warm environments. A very high dew point indicates a large amount of water vapor in the air. The NWS Tampa Bay region, for example, can experience summer dew points above 80°F. That does not mean 80°F is a universal threshold for every location.
Suppose grass cools overnight. If the grass surface temperature falls below the dew point of the nearby air, water vapor can condense on the surface.
Surface temperature falls below the dew point, and condensation can occur. This is dew. Air temperature at weather-station height does not need to fall below the dew point for every individual surface to become cool enough for condensation.
| Stage | What Happens |
|---|---|
| Surface Cools Below Dew Point | A surface such as grass loses heat overnight |
| Condensation Can Occur | Water vapor condenses on the cooled surface as dew |
No. "Dew point" is a temperature. "Relative humidity" is a percentage. They describe related but different aspects of atmospheric moisture. Example: Dew point 65°F, Relative humidity 70%.
If you know air temperature and dew point, you can reverse the vapor-pressure relationship. CalculateThisWay uses the same consistent Magnus coefficients in both directions. If the dew point is close to the air temperature, the relative humidity will be high. If the dew point is far below the air temperature, the RH will generally be lower.
Overnight, air often cools. If moisture content stays relatively steady while temperature falls toward the dew point, relative humidity rises. After sunrise, temperature may increase while dew point changes much less. Relative humidity then drops. This does not necessarily mean all of the atmospheric moisture disappeared.
Meteorologists use dew point to understand moisture. Moisture can influence cloud formation, fog, precipitation potential, thunderstorm environments, and human comfort. But dew point alone does not predict whether a storm will happen. Weather development depends on many atmospheric variables.
Dew point describes atmospheric moisture. Heat index estimates how hot conditions feel using temperature and humidity. They are not interchangeable. A person concerned about dangerous heat should use official NWS heat guidance rather than treating one dew-point number as a complete heat-risk assessment.
Dew Point Calculator focuses on atmospheric moisture. Wind Chill Calculator focuses on the cooling effect of cold air and wind on exposed skin. They answer completely different weather questions.
Dew point tells you how much moisture is present in the air in a way that is often easier to compare than relative humidity alone. CalculateThisWay lets you move in both directions: temperature + RH → dew point, and temperature + dew point → relative humidity. The calculator also shows the temperature-dew-point spread and explains what the result actually means.
The examples below are calculated live in JavaScript with the exact formula used by the calculator above, including one combination that falls outside the formula's valid range.
Air Temperature: 80°F. Relative Humidity: 50%.
About what dew point would you expect, and is it in the "dry," "sticky," or "muggy" general comfort range?
At 80°F and 50% relative humidity, the dew point works out to approximately 60°F, right at the edge of the "increasingly sticky" range in the general NWS warm-season comfort reference.
I want dew point, relative humidity, or a temperature-dew-point comparison for atmospheric moisture.
I want the official NWS cold-weather feels-like temperature from air temperature and wind speed.
I want to convert temperature or other units on their own, outside a weather context.
Dew point is the temperature to which air must be cooled, at constant pressure and moisture content, for it to become saturated with water vapor. That definition comes from the National Weather Service. A higher dew point means more moisture is present in the air.
Enter an air temperature and a relative humidity into the calculator above, choose Fahrenheit or Celsius, and press Calculate. The calculator applies a NOAA/NCEP-style Magnus equation and shows the result in both Fahrenheit and Celsius.
CalculateThisWay uses a Magnus-type equation consistent with NOAA/NCEP methodology: e = (RH/100) × 6.1365 × exp(17.502T / (240.97 + T)), then dew point = 240.97 × ln(e/6.1365) / (17.502 − ln(e/6.1365)), with temperature in Celsius.
Dew point describes how much moisture is in the air. The higher the dew point, the more water vapor the air is holding, regardless of the current air temperature.
Relative humidity is the percentage of moisture currently in the air compared with the maximum amount the air could hold at its current temperature. It changes with temperature even when moisture content stays the same.
Dew point is a temperature. Relative humidity is a percentage. Dew point describes actual atmospheric moisture more directly, while relative humidity also depends heavily on the current air temperature.
Because dew point does not change simply because the air warms or cools the way relative humidity does. A steady dew point generally means the moisture content of the air has stayed about the same, even if the temperature changes.
When air temperature equals the dew point, the air is approximately saturated and relative humidity is approximately 100%. That does not guarantee rain. It simply means the air has reached saturation at that temperature and moisture content.
At the same observation point under ordinary atmospheric conditions, no. Dew point should not exceed the actual air temperature. If entries suggest otherwise, check the values rather than trusting the result.
Dew point depression is air temperature minus dew point. A smaller spread generally indicates air closer to saturation, while a larger spread means the temperature is farther above the dew point.
Enter an air temperature and a dew point into the Find Relative Humidity mode above. The calculator reverses the same Magnus-type vapor-pressure relationship used for dew point, with both temperatures converted to Celsius first.
The National Weather Service Tampa Bay office describes dew points at or below about 55°F as relatively dry and comfortable in general warm-season terms. This is a general comfort reference, not a medical threshold, and individual perception varies.
A 55°F dew point sits at the drier edge of the National Weather Service's general warm-season comfort reference, often felt as comfortable rather than sticky.
A 60°F dew point usually brings noticeable moisture compared with very dry air. In the general NWS warm-season comfort framework it falls in the range where conditions can begin to feel sticky.
A 65°F dew point sits at the upper edge of the National Weather Service's general comfort reference, often described as where conditions start containing a lot of moisture and becoming increasingly oppressive in warm weather.
A 70°F dew point indicates substantial atmospheric moisture. Warm weather with dew points in this range often feels muggy. Dew point alone does not determine heat danger; use official Heat Index, HeatRisk, and NWS warnings for that.
A 75°F dew point reflects a large amount of water vapor in the air and is generally associated with very humid, muggy conditions in warm weather, particularly in humid regions.
Yes, particularly in very humid warm environments such as the Gulf Coast and parts of Florida. The NWS Tampa Bay region, for example, can see summer dew points above 80°F. That does not make 80°F a universal threshold everywhere.
Not by itself. A high dew point indicates abundant atmospheric moisture, which is one ingredient weather systems can use, but it does not predict whether or when precipitation will occur.
A small temperature-dew-point spread can indicate air closer to saturation, but fog also depends on cooling, wind, mixing, terrain, and moisture supply. Dew point is one piece of information, not a guaranteed fog forecast.
When a surface such as grass cools overnight below the dew point of the nearby air, water vapor can condense on that surface. The air temperature at weather-station height does not need to fall below the dew point for an individual surface to become cool enough for dew.
Overnight, air often cools toward the dew point while moisture content stays fairly steady, which raises relative humidity. After sunrise, temperature rises faster than dew point, so relative humidity drops even though much of the moisture is still present.
Warmer air can hold more water vapor before reaching saturation. If moisture content stays the same while temperature increases, the air is farther from saturation, so relative humidity falls.
Yes. If moisture content remains steady, warming the air generally lowers relative humidity and cooling it generally raises relative humidity, even while the dew point itself changes only modestly.
No. Dew point is a temperature, expressed in degrees Fahrenheit or Celsius. Relative humidity is the percentage value.
No. Dew point describes atmospheric moisture. Heat index estimates how hot conditions feel using temperature and humidity together. They are related but not interchangeable.
Not by itself. For heat-safety decisions, use official National Weather Service Heat Index, HeatRisk, and heat warnings rather than a single dew-point number.
Yes. Select Celsius for the air temperature, and the calculator converts internally and displays the dew point in both Fahrenheit and Celsius.
Yes. Fahrenheit is the default unit, and results are always shown in both Fahrenheit and Celsius.
A Magnus-type equation consistent with NOAA/NCEP MADIS methodology, using the coefficients 6.1365, 17.502, and 240.97, computed in Celsius internally.