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Calculation Machine

Dew Point Calculator

Dew point from temperature and humidity.

Reviewed by the Calculation Machine team · How we check our maths

Your values

ⓘ Live results

Results
Dew point
18.19 °C
In Fahrenheit
64.74 °F
Comfort level
Humid
Spread from air temp
5.81 °C
Fog likely if temp falls to
18.2 °C

Working

  1. 1α = ln(70/100) + (17.625 × 24)/(243.04 + 24) = 1.2274

Quick answer

Dew point is the temperature at which air becomes saturated; above 20°C (68°F) most people find the air oppressive.

The formula

Td = (b·α) ÷ (a − α), α = ln(RH/100) + aT/(b+T)

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Air temperature24 °C
  • Relative humidity70 %

Result

  • Dew point18.19 °C
  • In Fahrenheit64.74 °F
  • Comfort levelHumid
  • Spread from air temp5.81 °C
  • Fog likely if temp falls to18.2 °C

How to use the Dew Point Calculator

  1. 1Enter the air temperature in Celsius.
  2. 2Enter relative humidity.
  3. 3Read the dew point and comfort level.

Frequently asked questions

Why is dew point better than humidity?

Relative humidity depends on temperature; dew point is an absolute measure of moisture, so 20°C dew point feels muggy anywhere.

When does condensation form?

When a surface is at or below the dew point — that's why cold glasses sweat and windows fog.

About this calculator