Dew Point Calculator

Temperature · humidity · dew point

See the moisture in your air

Enter any two values to calculate the third. Leave the value you want calculated blank, then review the complete air state and a plain-language description of how the humidity may feel.

1. Inputs

Enter two known values

Solve: Dew point temperature

Type two measurements and leave the value you want calculated empty.

Air temperatureCurrent dry-bulb temperature

Supported air-temperature range: −45°C to 60°C.

Relative humidityMoisture relative to saturation

Enter a value greater than 0% and no more than 100%.

Dew point temperatureTemperature where condensation begins

Dew point cannot be above the air temperature.

Will calculate: Dew point temperatureThe other two values will be used as the known measurements.

2. Result

Your air snapshot

Example

Dew point temperature13.22 °C

55.8 °F · 286.37 K

How the air may feel

Increasingly sticky

This dew point can feel increasingly sticky, especially during warm evenings.

Based mainly on dew point. Wind, sun, clothing, activity, and personal sensitivity can change how it feels.

Air temperature: 20 °C68 °F
Relative humidity: 65%Current saturation level
Dew point: 13.22 °C55.8 °F

6.78 °C temperature–dew point spreadThe air is not currently close to saturation; condensation begins after further cooling.

General outdoor comfort guidance only: perception varies by conditions and person, and this is not a medical or heat-safety alert.

3. Moisture details

What the air contains

Calculated

Water vapor pressure: 1,516.7 Pa1.5167 kPa
Saturation vapor pressure: 2,333.4 Pa2.3334 kPa
Absolute humidity: 11.2111 g/m³Water-vapor mass per cubic meter of air
Condensation threshold: 13.22 °CSurfaces at or below this temperature may collect moisture

Formula, range, and assumptions

The calculator uses the Magnus relationship with a = 17.625 and b = 243.04°C, then rearranges the same relationship for whichever value is missing.

γ = ln(RH/100) + aT/(b+T) · Td = bγ/(a−γ)

Air temperature is limited to −45°C through 60°C.
Relative humidity must be greater than 0% and at most 100%.
Vapor pressure and absolute humidity are derived from the same calculated moist-air state without assuming a total atmospheric pressure.
This is not a frost-point, wet-bulb, mold-risk, or weather-forecast calculation.

Atmospheric moisture

Read moisture separately from the day's air temperature

Relative humidity can rise as air cools even when its water-vapour content changes little. Dew point supplies a temperature-based view of that moisture and helps frame comfort, condensation, and fog questions without pretending to be a forecast.

Side-by-side guide · Atmospheric moisture

Choose the pair that matches the observation

At the dew point: Relative humidity reaches 100%
Physical ordering: Dew point ≤ air temperature
Model air range: −45 °C to 60 °C

Air temperature + relative humidity
Use a collocated temperature and RH reading to estimate dew point. This is the usual path for a weather station or room sensor whose moisture channel reports percent RH.
Air temperature + dew point
Use a forecast or instrument pair to recover relative humidity. Dew point cannot exceed air temperature within the calculator's unsaturated-to-saturated model.
Relative humidity + dew point
Use these values to estimate air temperature, provided the combination stays inside the supported range. This is an inverse calculation, not a substitute for a calibrated thermometer.

Read moisture separately from the day's air temperature: The workbench solves one missing quantity from the other two rather than requiring one fixed input order.

Why two afternoons with 50% RH can feel different

Relative humidity is a ratio between the vapour present and the saturation amount at the current temperature. Because warm air has a different saturation vapour pressure from cool air, the same percentage does not imply the same quantity of water vapour. The National Weather Service gives a useful contrast: a cold 30 °F day at 100% relative humidity can contain less moisture and feel less muggy than an 80 °F day with a 60 °F dew point and 50% relative humidity.

Dew point asks how far the air would need to cool, at constant pressure, to reach saturation. A higher dew point generally signals more atmospheric moisture. If the dew point approaches the air temperature, the temperature–dew-point spread narrows and saturation becomes closer; that can support condensation or fog, but it does not by itself prove either will occur at a particular surface or location.

Choose the pair that matches the observation

The workbench solves one missing quantity from the other two rather than requiring one fixed input order.

Air temperature + relative humidity

Use a collocated temperature and RH reading to estimate dew point. This is the usual path for a weather station or room sensor whose moisture channel reports percent RH.

Air temperature + dew point

Use a forecast or instrument pair to recover relative humidity. Dew point cannot exceed air temperature within the calculator's unsaturated-to-saturated model.

Relative humidity + dew point

Use these values to estimate air temperature, provided the combination stays inside the supported range. This is an inverse calculation, not a substitute for a calibrated thermometer.

Use the result for the right kind of decision

Dew point is informative in several settings, but each setting needs additional evidence.

For outdoor comfort, NWS summer guidance describes dew points at or below about 55 °F as generally dry and comfortable, 55–65 °F as increasingly sticky, and 65 °F or above as increasingly oppressive. These are broad perceptions, not health thresholds.
For surface condensation, compare the calculated dew point with the actual surface temperature. Air dew point alone cannot reveal a window, pipe, wall cavity, or product surface temperature.
For fog, a small spread indicates air near saturation, but wind, mixing, terrain, radiation, and local moisture supply still affect formation and persistence.
For cold-weather exposure, dew point is not wind chill. Use the wind chill calculator when air temperature and wind speed are the relevant variables.

What the Magnus approximation can and cannot promise

Keep both sensors together
Temperature and RH should describe the same air at the same time. A shaded thermometer and a sun-heated humidity enclosure can create a mathematically tidy but physically mismatched result.
Respect the calculation domain
This implementation uses a Magnus-type saturation-vapour-pressure approximation and accepts air temperature from −45 °C through 60 °C, with RH greater than 0% and no more than 100%. It is not a full steam-table or cryogenic model.
Round to the instrument, not the equation
Sensor accuracy, response lag, siting, pressure assumptions, and calibration usually matter more than extra displayed decimals. Preserve the unrounded value for intermediate math, then report no finer than the observations justify.

Move between scales without changing the moisture question

The calculator accepts Celsius and Fahrenheit directly. If a separate report needs a stand-alone scale conversion, use the Celsius-to-Fahrenheit calculator or the reverse-direction Fahrenheit-to-Celsius calculator. Converting the temperature scale changes the numerical representation, not the physical moisture state.

For laboratory thermodynamic data expressed in kelvin, the kelvin-to-Celsius calculator can put a temperature on the scale used here. Do not enter a kelvin number as though it were degrees Celsius. And do not use a dew-point comfort label as an alert: heat illness, frost risk, ventilation design, and building-envelope analysis each require additional measurements and domain-specific guidance.

Important limitations

Dew Point Calculator is limited to the finite inputs, modes, and outputs stated for the Dew point, humidity, and air-temperature multi-solve method. Check air temperature unit, dew-point temperature unit, air temperature, relative humidity, and dew-point temperature, validation messages, the equation, and the stated display precision before relying on calculated quantity, air temperature, and relative humidity.

Review the stated scope, calculation method, assumptions, supported inputs, and effective dates, and obtain qualified advice before using a high-stakes result.

This formula passed its registered engineering tests and is published under an explicit site-owner policy authorization. No independent expert, QA, editorial, legal, or third-party review is claimed. Verify consequential results with a qualified professional.

Atmospheric moisture

Read moisture separately from the day's air temperature

Side-by-side guide · Atmospheric moisture

Choose the pair that matches the observation

At the dew point: Relative humidity reaches 100%
Physical ordering: Dew point ≤ air temperature
Model air range: −45 °C to 60 °C

Air temperature + relative humidity
Use a collocated temperature and RH reading to estimate dew point. This is the usual path for a weather station or room sensor whose moisture channel reports percent RH.
Air temperature + dew point
Use a forecast or instrument pair to recover relative humidity. Dew point cannot exceed air temperature within the calculator's unsaturated-to-saturated model.
Relative humidity + dew point
Use these values to estimate air temperature, provided the combination stays inside the supported range. This is an inverse calculation, not a substitute for a calibrated thermometer.

Read moisture separately from the day's air temperature: The workbench solves one missing quantity from the other two rather than requiring one fixed input order.

Why two afternoons with 50% RH can feel different

Choose the pair that matches the observation

The workbench solves one missing quantity from the other two rather than requiring one fixed input order.

Air temperature + relative humidity

Use a collocated temperature and RH reading to estimate dew point. This is the usual path for a weather station or room sensor whose moisture channel reports percent RH.

Air temperature + dew point

Use a forecast or instrument pair to recover relative humidity. Dew point cannot exceed air temperature within the calculator's unsaturated-to-saturated model.

Relative humidity + dew point

Use these values to estimate air temperature, provided the combination stays inside the supported range. This is an inverse calculation, not a substitute for a calibrated thermometer.

Use the result for the right kind of decision

Dew point is informative in several settings, but each setting needs additional evidence.

For outdoor comfort, NWS summer guidance describes dew points at or below about 55 °F as generally dry and comfortable, 55–65 °F as increasingly sticky, and 65 °F or above as increasingly oppressive. These are broad perceptions, not health thresholds.
For surface condensation, compare the calculated dew point with the actual surface temperature. Air dew point alone cannot reveal a window, pipe, wall cavity, or product surface temperature.
For fog, a small spread indicates air near saturation, but wind, mixing, terrain, radiation, and local moisture supply still affect formation and persistence.
For cold-weather exposure, dew point is not wind chill. Use the wind chill calculator when air temperature and wind speed are the relevant variables.

What the Magnus approximation can and cannot promise

Keep both sensors together
Temperature and RH should describe the same air at the same time. A shaded thermometer and a sun-heated humidity enclosure can create a mathematically tidy but physically mismatched result.
Respect the calculation domain
This implementation uses a Magnus-type saturation-vapour-pressure approximation and accepts air temperature from −45 °C through 60 °C, with RH greater than 0% and no more than 100%. It is not a full steam-table or cryogenic model.
Round to the instrument, not the equation
Sensor accuracy, response lag, siting, pressure assumptions, and calibration usually matter more than extra displayed decimals. Preserve the unrounded value for intermediate math, then report no finer than the observations justify.