Clausius Clapeyron Humidity Calculator

Enter Humidity Values

Air temperature

Air temperature unit

Atmospheric pressure

Pressure unit

Actual vapor input method

Dew point

Dew point unit

Known relative humidity (%)

Actual vapor pressure

Vapor pressure unit

Surface phase model

Custom latent heat (J/kg)

Decimal precision

Formula Used

The calculator uses the integrated Clausius Clapeyron relation for saturation vapor pressure.

e_s(T) = e₀ × exp[(L/R_v) × (1/T₀ − 1/T)] RH = (e_a / e_s) × 100 T_d = 1 / [1/T₀ − (R_v/L) × ln(e_a/e₀)] Absolute humidity = 2167 × e_a / T Mixing ratio = 0.62198 × e_a / (P − e_a)

Here, T is in Kelvin. Vapor pressure and atmospheric pressure use the same pressure base. The reference pressure is 0.61121 kPa at 273.15 K.

How to Use This Calculator

Enter the air temperature and select the correct temperature unit.
Enter atmospheric pressure. Use 101.325 kPa for standard sea level pressure.
Select the input method for actual vapor pressure.
Enter dew point, known relative humidity, or actual vapor pressure.
Select the liquid water, ice, or custom latent heat model.
Choose decimal precision and press the calculate button.
Use the CSV or PDF buttons to save the report.

Example Data Table

Air Temp (°C)	Dew Point (°C)	Pressure (kPa)	Relative Humidity	Absolute Humidity	VPD	Mixing Ratio
10.0	5.0	101.325	70.89%	6.68 g/m³	0.359 kPa	5.41 g/kg
25.0	16.0	101.325	56.80%	13.32 g/m³	1.394 kPa	11.45 g/kg
32.0	22.0	99.800	54.79%	19.04 g/m³	2.213 kPa	17.17 g/kg
5.0	-2.0	101.000	60.47%	4.11 g/m³	0.345 kPa	3.27 g/kg

Clausius Clapeyron Humidity Conversion Guide

Why vapor pressure matters

Humidity is not only a percent value. It is a pressure problem first. Warm air can support more water vapor than cold air. The Clausius Clapeyron equation estimates that saturation pressure from temperature. This calculator uses that pressure as the main reference. Then it compares real vapor pressure against the saturated value. The result is relative humidity, dew point, vapor pressure deficit, absolute humidity, and mixing ratio.

This method is useful in weather checks, drying rooms, labs, crop storage, and comfort studies. It also helps when a sensor gives dew point instead of relative humidity. You can enter dew point, known relative humidity, or direct vapor pressure. The tool converts each input into actual vapor pressure. It then builds the final humidity report from one consistent set of values.

What the results show

Saturation vapor pressure is the maximum water vapor pressure at the selected air temperature. Actual vapor pressure is the pressure already present in the air. Relative humidity is the actual pressure divided by the saturated pressure. Dew point is the temperature where the same air parcel would reach saturation.

Absolute humidity gives grams of water vapor per cubic meter. Mixing ratio gives grams of vapor per kilogram of dry air. Specific humidity gives grams of vapor per kilogram of moist air. Vapor pressure deficit shows the drying power of the air. A larger deficit means the air can accept more moisture.

Best practice

Use accurate temperature units. Check pressure units before calculating. Sea level pressure is commonly near 101.325 kPa. Indoor work can often use the default pressure unless a precise mixing ratio is needed. For freezing conditions, use the ice surface option. For normal liquid water conditions, use the water option. Custom latent heat is available for advanced study.

The equation is an approximation. Real air can vary with impurities, non ideal behavior, and sensor limits. Still, it gives strong estimates for many conversion tasks. Use the exported report for notes, audits, or repeat checks. Keep input units with every result. Run several cases to compare moisture changes under different temperatures, pressures, and dew points clearly.

FAQs

What does this calculator estimate?

It estimates saturation vapor pressure, actual vapor pressure, relative humidity, dew point, absolute humidity, mixing ratio, specific humidity, and vapor pressure deficit from your entered temperature and moisture data.

Why use the Clausius Clapeyron equation?

It links temperature with saturation vapor pressure. That makes it useful for estimating how much water vapor air can hold before condensation begins.

Can I calculate humidity from dew point?

Yes. Select the dew point input method. The tool converts dew point into actual vapor pressure, then compares it with saturation pressure at the air temperature.

Can I use known relative humidity?

Yes. Select the relative humidity method. The tool multiplies saturation vapor pressure by the entered percent value to estimate actual vapor pressure.

What pressure should I enter?

Use measured local pressure when available. For many standard examples, 101.325 kPa is acceptable. Pressure mainly affects mixing ratio and specific humidity.

When should I use the ice option?

Use it for freezing conditions where vapor pressure over ice is more relevant. The ice model uses a different latent heat value.

Why is relative humidity above 100%?

That can happen when entered dew point or vapor pressure exceeds the saturation value at the air temperature. It may show supersaturation or an input error.

Are CSV and PDF reports included?

Yes. After entering values, use the CSV or PDF buttons. The report includes all calculated output metrics and the selected model details.