Dew Point Calculator

You can use this dew point calculator to determine the dew point temperature (Tdew) according to the temperature of the air (T) and the relative humidity (RH).

You can calculate the dew point in three simple steps:

  1. Select the temperature unit between Fahrenheit (°F), Celsius (°C), or Kelvin (K).
  2. Input the details of the relative humidity and the temperature of the air.
  3. Click on the "Calculate" link to determine the dew point.
Dew Point Calculator

°F

%

Dew Point Calculator Results
Results
 Fahrenheit (°F)Celsius (°C)Kelvin (K)
Dew Point (Tdew): ---

Dew Point Chart

Temperature (°F)Relative Humidity (%)
404550556065707580859095100
100 71.3 74.8 78 80.9 83.6 86.1 88.4 90.6 92.7 94.7 96.5 98.3 100
99 70.4 73.9 77.1 80 82.7 85.1 87.5 89.7 91.7 93.7 95.5 97.3 99
97 68.6 72.1 75.2 78.1 80.8 83.3 85.6 87.7 89.8 91.793.695.397
95 66.9 70.3 73.4 76.3 78.9 81.4 83.7 85.8 87.8 89.891.693.395
93 65.1 68.5 71.6 74.4 77 79.5 81.7 83.9 85.9 87.889.691.393
91 63.3 66.7 69.8 72.6 75.2 77.6 79.8 82 84 85.887.689.491
90 62.4 65.8 68.8 71.6 74.2 76.6 78.9 81 83 84.986.788.490
88 60.6 64 67 69.8 72.4 74.7 77 79.1 81 82.984.786.488
86 58.9 62.2 65.2 67.9 70.5 72.9 75.1 77.1 79.1 8182.784.486
84 57.1 60.4 63.4 66.1 68.6 71 73.2 75.2 77.2 7980.782.484
82 55.3 58.6 61.5 64.2 66.7 69.1 71.2 73.3 75.2 7778.880.482
81 54.4 57.7 60.6 63.3 65.8 68.1 70.3 72.3 74.2 76.177.879.481
79 52.6 55.9 58.8 61.5 63.9 66.2 68.4 70.4 72.3 74.175.877.479
77 50.8 54 56.9 59.6 62.1 64.3 66.5 68.5 70.4 72.173.875.577
75 49.1 52.2 55.1 57.7 60.2 62.4 64.6 66.5 68.4 70.271.973.575
74 48.2 51.3 54.2 56.8 59.2 61.5 63.6 65.6 67.4 69.270.972.574
72 46.4 49.5 52.4 55 57.4 59.6 61.7 63.6 65.5 67.268.970.572
70 44.6 47.7 50.5 53.1 55.5 57.7 59.8 61.7 63.5 65.366.968.570
68 42.8 45.9 48.7 51.2 53.6 55.8 57.9 59.8 61.6 63.36566.568
66 41 44.1 46.8 49.4 51.7 53.9 55.9 57.9 59.7 61.46364.566
64 39.2 42.3 45 47.5 49.9 52 54 55.9 57.7 59.46162.564
63 38.3 41.4 44.1 46.6 48.9 51.1 53.1 55 56.7 58.46061.563
61 36.5 39.5 42.3 44.7 47 49.2 51.2 53 54.8 56.55859.661
59 34.7 37.7 40.4 42.9 45.2 47.3 49.2 51.1 52.8 54.556.157.659
57 33 35.9 38.6 41 43.3 45.4 47.3 49.2 50.9 52.554.155.657
Very Uncomfortable Uncomfortable OK for most Comfortable Dry

What is Dew Point?

The temperature to which air needs to be cooled before it reaches saturation is known as the dew point temperature. When air reaches the dew point, the ambient water vapor condenses, forming fog or dew.

There is a close relationship between dew point and relative humidity (RH), the latter of which is the ratio of the water vapor pressure in an air parcel to the saturation pressure of the water vapor in that same parcel at a specific temperature. RH is expressed as a percentage.

When the air temperature (T) and the dew point are the same, the relative humidity is 100 percent. A further drop in temperature will result in the formation of condensation and liquid water.

Evaluating dew point is often considered to be a more accurate method of measuring air comfort and humidity than relative humidity because it is an absolute measurement, while relative humidity is not.

An equation that is frequently employed to determine dew point according to the T and RH, is as follows:

Tdew = (237.3 × [ln(RH/100) + ( (17.27×T) / (237.3+T) )]) / (17.27 - [ln(RH/100) + ( (17.27×T) / (237.3+T) )])

Where:

Tdew = dew point temperature in degrees Celsius (°C), T = air temperature in degrees Celsius (°C), RH = relative humidity (%), ln = natural logarithm.

Example of a Dew Point Calculation

Let's say we have an air temperature of 20°C (68°F) and relative humidity of 70%. We can calculate the dew point temperature as follows:

Tdew = (237.3 × [ln(70/100) + ( (17.27×20) / (237.3+20) )]) / (17.27 - [ln(70/100) + ( (17.27×20) / (237.3+20) )])

Tdew ≈ 14.36°C, or 57.2°F.

You may also like to try our Wind Chill Calculator or / and the Heat Index Calculator

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