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Enter your values, then click Calculate result.How this calculator helps
Estimate liquid-water dew point from air temperature and relative humidity, with Celsius/Fahrenheit output and an explicit 0–50°C model boundary. Select Celsius or Fahrenheit for the air-temperature field. Relative humidity is entered as a percentage, so fifty percent is 50 rather than 0.5. Use measurements representing the same place and time. A thermometer in direct sunlight and a humidity sensor in another room do not describe one air parcel. This page does not retrieve a weather observation or independently check sensor calibration.
How to use it
- 1
Choose the correct input basis for dew point calculator and enter the values described below. The demonstration defaults are examples, not independently verified personal measurements.
- 2
Review meaning of dew point before submitting. Match the selected units and roles to the original source record, including any signs or percentage conventions.
- 3
Click Calculate result to submit the current inputs. Editing a field preserves the previous submitted output until you calculate again; the status message identifies that pending change.
- 4
Compare the labeled result with the worked example and independent verification checks. Review practical interpretation before copying it into another worksheet.
Formula and methodology
γ = ln(RH/100) + 17.625T/(243.04+T). Dew point = 243.04γ/(17.625−γ), with T in °C. Both air temperature and calculated dew point must lie in 0–50°C.
The calculator applies the displayed arithmetic to the values entered on this device. It does not silently load a local tax rate, currency conversion or commercial assumption.
Worked calculation example
At 25°C and 50% relative humidity, the formula gives approximately 13.85761254°C, or 56.94370257°F. At 100% relative humidity, dew point equals the air temperature. A dry input that would give a subzero dew point is rejected under this worksheet’s narrower liquid-water scope.
How to interpret your result
The displayed Magnus equation is an approximation with stated constants, not an exact thermodynamic solver. This implementation deliberately accepts only air temperatures from zero to fifty Celsius and results in that same range. It therefore avoids claiming a frost-point calculation or extrapolating to subzero dew points. A wider weather model could use different phase assumptions and coefficients; this worksheet does not switch them silently.
For different inputs or formulas, use VPD Calculator — Air, Leaf and Relative Humidity; Electricity Usage Calculator.
Related questions this calculator covers
- dew point calculator
- dewpoint calculator
- how to calculate dew point
Scenario comparison
| Scenario | What it shows |
|---|---|
| Saturation | 25°C and 100% RH returns 25°C. |
| Moderate humidity | 25°C and 50% RH gives about 13.8576°C. |
| Dry boundary | a calculated negative dew point is rejected. |
Common mistakes to avoid
- Entering 0.5 instead of 50 for fifty percent humidity.
- Combining sensors from different places or times.
- Interpreting liquid-water dew point as frost point.
At full humidity, check that dew point equals input temperature. For the default example, substitute the calculated dew point into the ratio of Magnus saturation expressions and recover roughly 50% humidity. Compare a Fahrenheit and equivalent Celsius input to verify the unit conversion. That check tests the chosen approximation, not the accuracy of the sensors.
Authoritative reference and additional source reference. Alduchov and Eskridge’s 1996 Magnus-form paper supplies the coefficient context; the NWS page explains the related air-temperature/humidity task and uses its own formulation. SolvePilot uses the explicitly displayed 17.625 and 243.04 coefficients within its narrower 0–50°C liquid-water scope. References reviewed on 5 October 2026 by Mohammad Qasim; no sensor calibration or building assessment is performed.What can affect the result?
Temperature and humidity inputs
Select Celsius or Fahrenheit for the air-temperature field. Relative humidity is entered as a percentage, so fifty percent is 50 rather than 0.5. Use measurements representing the same place and time. A thermometer in direct sunlight and a humidity sensor in another room do not describe one air parcel. This page does not retrieve a weather observation or independently check sensor calibration.
Meaning of dew point
Dew point is the temperature at which the modeled air reaches saturation when cooled without changing its water-vapour amount. It is a temperature, not a percentage. Relative humidity depends on temperature, so two air samples at equal relative humidity can have different dew points. The temperature-minus-dew-point row shows the modeled gap but does not directly measure condensation on a particular object.
Liquid-water approximation
The displayed Magnus equation is an approximation with stated constants, not an exact thermodynamic solver. This implementation deliberately accepts only air temperatures from zero to fifty Celsius and results in that same range. It therefore avoids claiming a frost-point calculation or extrapolating to subzero dew points. A wider weather model could use different phase assumptions and coefficients; this worksheet does not switch them silently.
Saturation and invalid cases
A relative humidity of one hundred percent should return the air temperature. Zero humidity makes the logarithm undefined and is rejected. Values above one hundred percent are also outside this model. Very low humidity can give a negative modeled dew point even while air is warm; that case receives a scope error, not a fabricated zero result. The input boundary is visible before using the worksheet.
Practical interpretation
Condensation requires comparing an actual surface temperature with the relevant air dew point. Surface gradients, ventilation and moisture sources can change local conditions. This result does not predict mold growth, certify a building envelope or establish heat-stress risk. Keep the measured air temperature, humidity, sensor location and time with any saved output. Sensor uncertainty often matters more than the last displayed decimal.
Privacy and browser processing
Values entered on this page are processed in the current browser session. SolvePilot does not require an account and does not receive the values entered into the calculator. Refreshing or closing the page clears the working values unless the browser itself restores a previous session. Avoid entering identifying or account information because the calculation needs summary values only.
Accuracy and verification
Accuracy depends first on input quality. Confirm definitions, scales, dates and source information before entering a value. Keep an independent record of any result used for planning because this page does not create an official statement or retain a calculation history.
Limits of this estimate
Condensation requires comparing an actual surface temperature with the relevant air dew point. Surface gradients, ventilation and moisture sources can change local conditions. This result does not predict mold growth, certify a building envelope or establish heat-stress risk. Keep the measured air temperature, humidity, sensor location and time with any saved output. Sensor uncertainty often matters more than the last displayed decimal.
Sources and review information
Frequently asked questions
Can I use Fahrenheit?＋
Yes. Input Fahrenheit is converted to Celsius for the formula, then dew point is shown in both temperature units.
Why is a subzero dew point rejected?＋
This worksheet intentionally limits its liquid-water model to air and dew-point temperatures from 0–50°C. It does not supply a frost model.
What happens at 100% humidity?＋
The calculated dew point equals the air temperature within floating-point rounding.
Can I enter zero humidity?＋
No. The formula contains ln(RH/100), which is undefined at zero.
Does the result prove a surface will condense?＋
No. You also need the surface temperature and conditions at that surface. The calculator uses air measurements only.