A walkthrough, end to end.
- 1
Enter the air temperature and relative humidity.
- 2
Pick units: Celsius or Fahrenheit.
- 3
See the dew point — the temperature at which water vapor would condense.
Magnus-Tetens dew point
γ(T, RH) = ln(RH/100) + (a·T)/(b+T). Td = (b·γ) / (a−γ). With a = 17.625, b = 243.04 °C.
What you can do with this.
Comfort assessment
Td above 65°F (18°C) feels muggy; above 75°F (24°C) is oppressive.
Condensation risk
Surfaces below dew point will condense moisture.
HVAC sizing
Engineers use dew point for dehumidification design.
Weather forecasting
Stable dew point indicates a moist air mass.
Painting & coatings
Many finishes require surface ≥ 5°F above dew point.
Greenhouse management
Avoid plant disease by managing leaf-wet duration.
Aviation
Dew-point spread predicts fog formation.
Dew point 2026 — what's current
Magnus formula is the standard simplification.
Frequently asked.
Magnus formula is accurate for −45°C to 60°C, ±0.4°C error.
Below ~12°C (54°F) is dry; above 18°C (65°F) feels humid.
No. All math runs in your browser.
Different measures — dew point is at constant pressure, wet bulb involves evaporative cooling.