Frost Point Calculator

Convert humidity into frost point with confidence. Choose units, compare methods, and view key pressures. Ideal for aviation, HVAC, labs, and winter forecasting tasks.

Calculator
Pick the inputs you trust most.
Output is shown in this unit.
Higher precision is useful for validation.
Used to estimate vapor pressure from humidity.
%
Valid range: (0, 100].
Assumes saturation over liquid water at dew point.
Use partial pressure of water vapor.
Formula used

The calculator first finds the actual water vapor pressure e, then solves for the temperature where the saturation vapor pressure over ice matches e. Temperatures are in °C and pressure is in hPa.

Saturation over liquid water
esw(T) = 6.112 · exp( (17.62·T) / (243.12 + T) )
Saturation over ice
esi(T) = 6.112 · exp( (22.46·T) / (272.62 + T) )
Actual vapor pressure
e = (RH/100) · esw(Ta) for Air temperature + RH mode
Frost point from vapor pressure
Tf = 272.62·ln(e/6.112) / (22.46 − ln(e/6.112))

These coefficients are widely used for practical meteorology and instrumentation.

How to use this calculator
  1. Select a calculation mode based on your available measurements.
  2. Enter values and choose appropriate units for temperature or pressure.
  3. Set the output unit and decimal precision for reporting.
  4. Click Calculate Frost Point to show results above the form.
  5. Use Download CSV or Download PDF for records.
Example data table
Mode Air temperature Relative humidity Dew point Vapor pressure Approx. frost point
Air temperature + RH -5 °C 70% — — ≈ -8.6 °C
Air temperature + RH 2 °C 55% — — ≈ -3.5 °C
Dew point — — -10 °C — ≈ -13.2 °C
Vapor pressure — — — 3.5 hPa ≈ -12.1 °C
Vapor pressure — — — 0.8 kPa ≈ 4.8 °C
Values are illustrative; your outputs depend on units and rounding.
Note: In very dry air or extremely low pressures, frost point calculations can become sensitive.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.