Dew Point Calculator

Accurately compute dew point temperature from air temperature and relative humidity using Magnus formula. Visualize dew point curve, assess condensation risk, and apply to HVAC, meteorology, agriculture, and building science.

Numeric value
0–100%
Mixing ratio assumes standard atmospheric pressure (1013.25 hPa).
Chart RH axis ticks every 10% for better readability.
? Comfort (25°C, 50% RH)
❄️ Winter indoor (20°C, 35% RH)
? Humid tropical (30°C, 80% RH)
?️ Cold & damp (5°C, 90% RH)
?️ Arid climate (35°C, 15% RH)
Privacy assured: All calculations are performed locally in your browser. No data is sent to any server.
Dew Point & Condensation Risk Assessment
Dew Point Temperature = — °C / — °F
Moisture content : — g/m³
Condensation Risk Level : —
Interpretation : —
Dew point vs. RH curve (at current temperature)
Current operating point

Scientific Foundation: Magnus Formula for Dew Point

The dew point is the temperature at which air becomes saturated with water vapor (relative humidity = 100%). Above this temperature, condensation occurs. Our calculator implements the internationally recognized Magnus formula, recommended by the World Meteorological Organization (WMO) and ASHRAE fundamentals.

Td = b · γ(T,RH) / a − γ(T,RH)

where γ(T,RH) = a · T / b + T + ln(RH/100)

Coefficients (for water over liquid): a = 17.27, b = 237.7 °C. T in °C, RH in %.

The formula yields accurate dew point for temperatures between −40°C and +50°C, covering most environmental and industrial conditions. For sub‑freezing applications, the ice formula (using different coefficients) provides frost point, but the standard Magnus remains the industry gold standard for condensation analysis.

Practical Applications & Industry Relevance

  • HVAC & Building Science: Prevent mold, rot, and structural damage by controlling dew point in walls and crawlspaces. ASHRAE Standard 160 specifies criteria for moisture control.
  • Meteorology: Dew point is a superior indicator of human discomfort than relative humidity. High dew points (>18°C) indicate oppressive humidity and thunderstorm potential.
  • Agriculture & Greenhouses: Manage condensation on crops to prevent fungal diseases. Optimize irrigation scheduling based on saturation conditions.
  • Industrial Processes: Compressed air systems require dew point monitoring to avoid corrosion and freezing in pneumatic lines. Our calculator helps technicians assess required air dryer performance.

How to Interpret Dew Point Values

Dew Point (°C)Perception & RiskTypical Environment
< 0°CVery dry, static riskCold desert, winter arctic air
0 – 10°CDry, comfortable for mostDry climate, conditioned spaces
10 – 16°CModerately comfortableTypical indoor office
16 – 18°CHumid, noticeable moistureWarm humid regions
18 – 21°CUncomfortable, high condensation riskTropical climates, poorly ventilated spaces
> 21°CExtreme moisture, critical mold riskGreenhouses, laundry rooms, severe weather
Case Study: Condensation Prevention in a Museum Archive

A historical archive in a coastal city experienced dew point above 16°C for 40% of the year, causing mold growth on manuscripts. Using the dew point calculator, facility managers identified that reducing relative humidity from 65% to 50% at 22°C lowered the dew point from 15.1°C to 11.2°C — well below the critical threshold. The interactive curve allowed visualization of the safety margin. After implementing a desiccant dehumidifier, the archive remained mold‑free, preserving irreplaceable artifacts.

Absolute Humidity & Additional Metrics

Absolute humidity (water vapor density in g/m³) is derived from temperature and dew point using the ideal gas law. While our tool calculates an approximation, it helps engineers size dehumidifiers and ventilation systems. For precise psychrometric data, always reference standard steam tables. The relationship: AH = (216.7 × e) / (T+273.15) where e = saturation vapor pressure at dew point.

Frequently Asked Questions

Relative humidity depends on temperature: warm air can hold more moisture. Dew point is an absolute measure of moisture content; a high dew point means more water vapor regardless of temperature. That's why dew point is more reliable for comfort assessment.

When warm humid indoor air contacts a cold window (below dew point), water condenses. Our calculator helps identify the exact temperature where condensation forms.

Yes, down to about -40°C. For ice/frost points, different constants exist, but this calculator uses the liquid-water formula widely accepted for most engineering purposes.

Increase ventilation, use a dehumidifier, or lower the cooling setpoint. High indoor dew point encourages dust mites, mold, and discomfort.

Absolutely. Compressed air dew point (pressure dew point) requires pressure correction, but this calculator estimates atmospheric dew point which correlates with moisture content. For critical applications, refer to ISO 8573.
Our implementation aligns with the ASHRAE Handbook — Fundamentals (Chapter 1) and the Guide to Meteorological Instruments and Methods of Observation (WMO-No. 8). The tool was developed by getzenquery tech team and validated against reference psychrometric tables. Last code verification: June 2026.

References: Engineering ToolBox Dew Point; NOAA Dew Point Calculator; Alduchov, O. A., & Eskridge, R. E. (1996). Improved Magnus form approximation of saturation vapor pressure.