Dew point is the temperature at which air becomes saturated, so moisture starts to condense. Enter air temperature in °C and relative humidity. At 25°C (77°F) and 60% humidity, the dew point is about 16.7°C (62°F). The National Weather Service calls dew points of 55°F or lower dry and comfortable, 55–65°F sticky, and 65°F or higher oppressive. Fahrenheit users can convert with the unit converter first.
This dew point calculator estimates dew point temperature in Celsius from air temperature and relative humidity. Enter temp °C and RH percent to see how close the air is to saturation.
Weather learners, HVAC hobbyists, and outdoor planners use it to translate a humidity percent into a more intuitive moisture temperature. It uses a Magnus style approximation, not a full psychrometric lab instrument.
Dew point table
| Air temp | 30% RH | 50% RH | 60% RH | 80% RH |
|---|---|---|---|---|
| 10°C / 50°F | −6.8°C / 19.8°F | 0.1°C / 32.1°F | 2.6°C / 36.7°F | 6.7°C / 44.1°F |
| 20°C / 68°F | 1.9°C / 35.4°F | 9.3°C / 48.7°F | 12.0°C / 53.6°F | 16.4°C / 61.6°F |
| 25°C / 77°F | 6.2°C / 43.2°F | 13.8°C / 56.9°F | 16.7°C / 62.0°F | 21.3°C / 70.3°F |
| 30°C / 86°F | 10.5°C / 50.9°F | 18.4°C / 65.2°F | 21.4°C / 70.5°F | 26.2°C / 79.1°F |
| 35°C / 95°F | 14.8°C / 58.6°F | 23.0°C / 73.4°F | 26.0°C / 78.9°F | 31.0°C / 87.8°F |
Check: 80°F at 50% RH → 59.7°F, matching the NWS example (80°F with a 60°F dew point ≈ 50% RH). Values use the Magnus formula with 17.27 and 237.7.
How dew point is calculated
With a = 17.27 and b = 237.7, alpha equals a * T / (b + T) + ln(RH / 100). Dew point equals (b * alpha) / (a – alpha).
Worked example
Temperature 25°C, relative humidity 60 percent. Dew point is about 16.68°C.
| Input | Value |
|---|---|
| Temperature | 25°C |
| Relative humidity | 60% |
| Dew point | ~16.68°C |
How to use the fields
- Temperature must be in Celsius.
- Humidity is relative humidity percent from a sensor or weather report.
- Refresh inputs when conditions change through the day.
Reading comfort
Many people find dew points in the low teens °C more comfortable than dew points in the low twenties °C, even when the thermometer reading looks similar. Dew point focuses on moisture content rather than RH alone, which changes with temperature. For how hot it feels once humidity is high, see the heat index calculator, and for cold, windy days use the wind chill calculator.
How dew point feels (NWS)
| Dew point | Feel |
|---|---|
| 55°F (12.8°C) or lower | Dry and comfortable |
| 55–65°F (12.8–18.3°C) | Sticky, muggy in the evening |
| 65°F (18.3°C) or higher | Oppressive, lots of moisture in the air |
Source: National Weather Service: dew point vs. humidity. Formula reference: NOAA wet bulb and dew point sheet.
Indoor moisture checks
If indoor dew point is high, condensation risk on cold surfaces rises. Lower moisture sources, raise ventilation, or adjust cooling setpoints as needed. This calculator does not size dehumidifiers; it only estimates dew point from T and RH.
Do not mix an outdoor temperature with an indoor humidity reading. Both inputs should describe the same air mass. Bathrooms and kitchens spike RH locally; step away from showers and boiling pots when you want a room average.
For basement condensation checks, measure near the cold wall as well as at center room. A lower local temperature with the same moisture content raises relative humidity and can push surfaces to the dew point even when the center room feels fine.
Log a week of evening readings to see whether moisture problems are chronic or tied to weather systems.
Common mistakes
- Entering Fahrenheit in the Celsius field
- Using absolute humidity units instead of relative percent
- Comparing dew points from different times without matching locations
- Expecting frost point behavior below freezing from this liquid dew formula
Limitations
Results are an approximation for typical meteorological ranges. Extreme temperatures, sensor error, and local microclimates can shift real condensation behavior. Use the figure as a clear moisture signal, then confirm with local forecasts when safety matters.
For related unit and percent checks while you plan materials, try the unit converter or the percentage calculator.