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Relative Humidity Calculator

Work out relative humidity instantly with clear inputs, formula shown and shareable results.

About Relative Humidity Calculator

Relative humidity is the actual vapour pressure as a percentage of the saturation value at that temperature, computed here with the Magnus expression. Air at 22 C saturates at 26.5 hPa, so 15 hPa of actual vapour is 57% relative humidity with a dew point near 12.5 C. Warming air without adding moisture lowers relative humidity even though the water content is unchanged.

Formulas

Relative humidity

RH = 100 x actual vapour pressure / saturation vapour pressure

Magnus saturation

es = 6.112 exp(17.62T / (243.12 + T)) hPa

Worked example

With the default values below, Relative Humidity Calculator returns Relative Humidity of 56.87%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Air temperature
22 C
Actual vapour pressureminimum 0 hPa
15 hPa

Results

Relative Humidity
56.87%
Saturation Vapour Pressure
26.374 hPa
Implied Dew Point
13.05 C
Vapour Pressure Deficit
11.374 hPa

Step by step

  1. 1Values used
  2. 2Relative humidity
  3. 3Magnus saturation
  4. 4Relative Humidity= 56.87
  5. 5Saturation Vapour Pressure= 26.374 hPa
  6. 6Implied Dew Point= 13.05 C
  7. 7Vapour Pressure Deficit= 11.374 hPa

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why does indoor air feel dry in winter?

Because heating cold outdoor air raises its saturation pressure without adding moisture, so relative humidity collapses.

Is relative humidity the best comfort measure?

Dew point is better, because it tracks absolute moisture. 20 C dew point feels humid regardless of the relative reading.

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