Transparent method
The formula
Worked example
Example inputs
How to interpret the result
Temperature alone doesn't describe how humid a day actually feels, but dew point does directly, since a smaller gap between temperature and dew point means the air is closer to saturated and feels more oppressively humid regardless of what the raw temperature reading says on its own.
Before you rely on it
What to check
Compare the temperature-to-dew-point spread, not the raw temperature or humidity percentage alone, when judging how muggy conditions will actually feel.
The common error
Where people go wrong with dew point calculator
Judging humidity from the relative humidity percentage alone without checking dew point. A cool morning can show a high relative humidity percentage while actually feeling comfortable, because relative humidity depends on temperature in a way dew point doesn't.
Sensitivity evidence
How air temperature (°f) changes the dew point (°f)
| Air temperature (°F) | Dew point (°F) | Temperature-dew point spread |
|---|---|---|
| 60 | 43.8 | 16.2 |
| 68 | 51.2 | 16.8 |
| 75worked example | 57.7 | 17.3 |
| 83 | 65.1 | 17.9 |
| 90 | 71.6 | 18.4 |
Every input, tested
Which input moves the dew point (°f) most
| Input | Tested from | To | Dew point (°F) at each end | Swing |
|---|---|---|---|---|
| Air temperature (°F) | 68 | 83 | 51.2 to 65.1 | 13.9 (24%) |
| Relative humidity | 53.0% | 57.0% | 56.7 to 58.7 | 2 (3.5%) |
Two variables at once
Dew point (°F) by air temperature (°f) and relative humidity
| Air temperature (°F) \ Relative humidity | 51.0% | 55.0% | 59.0% |
|---|---|---|---|
| 60 | 41.8 | 43.8 | 45.6 |
| 68 | 49.2 | 51.2 | 53.1 |
| 75 | 55.6 | 57.7 | 59.7 |
| 83 | 63 | 65.1 | 67.2 |
| 90 | 69.4 | 71.6 | 73.7 |
Step by step
The worked example, input by input
| Input | Value used |
|---|---|
| Air temperature (°F) | 75 |
| Relative humidity | 55.0% |
| Dew point (°F) | 57.7 |
| Temperature-dew point spread | 17.3 |
Where the inputs come from
Enter the air temperature in degrees Fahrenheit and the relative humidity as a percent. The Magnus formula estimates the dew point, the temperature at which the air would be saturated and dew begin to form. Take the values from a thermometer and a hygrometer, or a weather report. The spread between temperature and dew point is also reported, which shows how close the air is to saturation.
Using the dew point (°f) in a real decision
When the spread shrinks to a few degrees, fog, dew or condensation are likely.
When the result stops applying
The formula is an approximation, most accurate for typical temperatures and humidities. Dew point does not change with temperature during the day unless moisture changes, while relative humidity does. Indoor condensation depends on surface temperatures, which can be below the air temperature. Sensors have error.
What to compare it with
See how it feels on the heat index calculator, cold effects on the wind chill page and heating and cooling demand on the degree days calculator. The temperature converter changes units, and the snow-to-liquid page relates to precipitation. Use a dehumidifier when indoor dew points stay high.
People also ask
Frequently asked questions
What is the dew point?
The temperature to which air must be cooled for water vapor to condense into dew, reflecting how much moisture the air holds.
Why is dew point better than relative humidity for comfort?
Because relative humidity depends on the temperature, while the dew point reflects the actual amount of moisture in the air.
What dew point feels muggy?
Above about 65 degrees Fahrenheit most people feel muggy, and above 70 it feels oppressive.