Dew Point Calculator
Calculate dew point temperature from relative humidity and air temperature instantly. Free online dew point calculator for weather forecasting, HVAC design, and condensation analysis.
Understanding Dew Point
Dew point is the temperature at which air becomes saturated with water vapor and condensation forms. Higher dew points indicate more moisture in the air. This measurement is crucial for weather prediction, HVAC systems, and comfort assessment.
Magnus Formula for Dew Point
Td = (b × α) / (a - α)
Where α = ln(RH/100) + (a × T) / (b + T)
a = 17.27, b = 237.7°C
T = air temperature, RH = relative humidity
The Magnus formula provides accurate dew point calculations for typical atmospheric conditions. Constants vary slightly between different formulations but produce similar results.
Comfort Level Table
| Dew Point (°F) | Dew Point (°C) | Human Comfort |
|---|---|---|
| Below 55°F | Below 13°C | Dry, comfortable |
| 55-59°F | 13-15°C | Comfortable for most |
| 60-64°F | 16-18°C | Slightly humid |
| 65-69°F | 18-21°C | Humid, noticeable |
| 70-74°F | 21-23°C | Very humid, uncomfortable |
| 75°F and above | 24°C and above | Oppressive, dangerous |
Condensation Prediction
When Condensation Forms
Condensation occurs when surface temperature falls below the dew point. Water vapor in the air changes to liquid on cold surfaces. This causes fog, dew on grass, and water droplets on cold drinks.
Building Moisture Control
Keep interior surfaces above dew point to prevent condensation in walls and attics. Proper insulation and ventilation reduce moisture problems. Vapor barriers prevent warm moist air from reaching cold surfaces.
HVAC System Design
Air conditioning coils must be below dew point to remove moisture. Supply air temperature affects indoor humidity levels. Proper sizing prevents short cycling and inadequate dehumidification.
Weather Forecasting
Dew point near air temperature indicates high humidity and possible fog or precipitation. Large temperature-dew point spread means dry air. Rising dew points often precede storms.
Dew Point Calculation Examples
Example 1: Moderate Conditions
Temperature: 25°C (77°F)
Relative Humidity: 60%
Dew Point: approximately 17°C (63°F)
Comfort: Slightly humid but acceptable
Example 2: High Humidity
Temperature: 30°C (86°F)
Relative Humidity: 80%
Dew Point: approximately 26°C (79°F)
Comfort: Very uncomfortable, oppressive
Example 3: Dry Conditions
Temperature: 35°C (95°F)
Relative Humidity: 20%
Dew Point: approximately 8°C (46°F)
Comfort: Dry heat, comfortable despite high temperature
Frequently Asked Questions
What is a comfortable dew point?
Dew points between 55°F and 59°F (13-15°C) feel comfortable to most people. Below 55°F feels dry and pleasant. Above 65°F (18°C) feels humid and uncomfortable for many individuals.
How does dew point differ from humidity?
Relative humidity changes with temperature while dew point remains constant for a given moisture content. Dew point directly indicates moisture amount. High relative humidity at low temperature may have lower dew point than moderate humidity at high temperature.
Why does dew form on grass in the morning?
Grass cools overnight through radiation. When grass temperature drops below the dew point, water vapor condenses into droplets. Clear nights promote more cooling and heavier dew formation.
What dew point causes fog?
Fog forms when air temperature equals dew point, creating 100% relative humidity. Temperature-dew point spread below 2.5°F (1.5°C) often indicates fog formation. Radiation fog commonly occurs on clear, calm nights.
Other Free Tools
Humidity Ratio Converter
Convert between relative humidity, absolute humidity, specific humidity, and humidity ratio. Free online humidity converter for HVAC, meteorology, and building climate control.
Wind Speed Converter
Convert wind speed between km/h, mph, knots, m/s, and Beaufort scale. Free online wind speed converter for meteorology, sailing, aviation, and weather analysis.
Rainfall Converter
Convert rainfall measurements between millimeters, inches, liters per square meter, and more. Free online precipitation converter for meteorology, hydrology, and agriculture.
Temperature Converter
Convert temperatures between Celsius, Fahrenheit, Kelvin, and Rankine. Free online temperature converter for weather, cooking, and science.
Temperature Interval Converter
Convert temperature difference units between Celsius, Fahrenheit, Kelvin, and Rankine. Free online converter for thermodynamics and HVAC.
Thermal Conductivity Converter
Convert thermal conductivity units — W/(m·K), BTU/(h·ft·°F), cal/(s·cm·°C), and more. Free online converter for insulation and heat transfer engineering.
Thermal Resistance Converter
Convert thermal resistance units — K/W, °C/W, °F·h/BTU, and more. Accurate online converter for HVAC, insulation, and electronics cooling.
Thermal Expansion Converter
Convert thermal expansion coefficients — per Kelvin, per Celsius, per Fahrenheit, and more. Free online converter for materials science and engineering.
Heat Transfer Coefficient Converter
Convert heat transfer coefficient units — W/(m²·K), BTU/(h·ft²·°F), and more. Accurate online converter for convection and HVAC engineering.
Heat Flux Density Converter
Convert heat flux density units — W/m², BTU/(h·ft²), cal/(s·cm²), and more. Free online converter for thermal engineering and solar energy.
Heat Density Converter
Convert heat density units — J/m³, BTU/ft³, cal/cm³, and more. Free online converter for combustion engineering and fuel analysis.
Length Converter
Convert length units instantly — meters, feet, inches, kilometers, miles, yards, and more. Free online length converter for everyday and scientific use.
Area Converter
Convert area units — square meters, acres, hectares, square feet, square kilometers, and more. Ideal for real estate and construction.
Volume Converter
Convert volume units — liters, gallons, milliliters, cubic feet, fluid ounces, and more. Free online volume converter for cooking and engineering.
Weight and Mass Converter
Convert weight and mass units — kilograms, pounds, grams, ounces, tons, and more. Accurate online weight converter for cooking, shipping, and science.
Speed Converter
Convert speed units — km/h, mph, m/s, knots, and more. Free online speed converter for travel, sports, physics, and engineering.
Acceleration Converter
Convert acceleration units — m/s², g-force, ft/s², Gal, and more. Accurate online converter for physics, aerospace, and mechanical engineering.
Time Converter
Convert time units — seconds, minutes, hours, days, weeks, months, years. Simple online time converter for everyday and scientific use.
Pressure Converter
Convert pressure units — pascals, bar, PSI, atmospheres, torr, and more. Free online pressure converter for engineering and science.
Energy Converter
Convert energy units — joules, calories, kilowatt-hours, BTU, electronvolts, and more. Free energy converter for physics and engineering.
Power Converter
Convert power units — watts, kilowatts, horsepower, megawatts, and more. Accurate online power converter for engineering calculations.
Density Converter
Convert density units — kg/m³, g/cm³, lb/ft³, lb/in³, and more. Free online density converter for material science, chemistry, and engineering.
Dynamic Viscosity Converter
Convert dynamic viscosity units — Pa·s, centipoise, poise, lb/(ft·s), and more. Free online converter for fluid mechanics and chemical engineering.
Kinematic Viscosity Converter
Convert kinematic viscosity units — m²/s, centistokes, stokes, ft²/s, and more. Accurate online converter for fluid dynamics and oil analysis.
Surface Tension Converter
Convert surface tension units — N/m, mN/m, dyne/cm, lbf/ft, and more. Free online converter for chemistry and materials science.
Mass Flux Density Converter
Convert mass flux density units — kg/(m²·s), lb/(ft²·s), and more. Free online mass flux converter for chemical engineering and filtration.
Linear Current Density Converter
Convert linear current density units — A/m, mA/cm, kA/m, and more. Free online converter for electromagnetics and electrical engineering.
Solution Concentration Converter
Convert solution concentration units — ppm, ppb, mg/L, percent, g/L, and more. Accurate online converter for chemistry and water treatment.
Molar Concentration Converter
Convert molar concentration units — mol/L, mmol/L, mol/m³, and more. Free online molarity converter for chemistry and biochemistry.
Ingredient Density Converter
Convert between volume and weight for common cooking ingredients using accurate density values. Free online ingredient converter for baking, cooking, and precise recipe scaling.