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Dew Point Calculator

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

You can calculate the dew point in three simple steps:

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

Dew Point Calculator Results

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

Dew Point Chart

Temperature (°F)	Relative Humidity (%)
Temperature (°F)	40	45	50	55	60	65	70	75	80	85	90	95	100
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	91.7	93.6	95.3	97
95	66.9	70.3	73.4	76.3	78.9	81.4	83.7	85.8	87.8	89.8	91.6	93.3	95
93	65.1	68.5	71.6	74.4	77	79.5	81.7	83.9	85.9	87.8	89.6	91.3	93
91	63.3	66.7	69.8	72.6	75.2	77.6	79.8	82	84	85.8	87.6	89.4	91
90	62.4	65.8	68.8	71.6	74.2	76.6	78.9	81	83	84.9	86.7	88.4	90
88	60.6	64	67	69.8	72.4	74.7	77	79.1	81	82.9	84.7	86.4	88
86	58.9	62.2	65.2	67.9	70.5	72.9	75.1	77.1	79.1	81	82.7	84.4	86
84	57.1	60.4	63.4	66.1	68.6	71	73.2	75.2	77.2	79	80.7	82.4	84
82	55.3	58.6	61.5	64.2	66.7	69.1	71.2	73.3	75.2	77	78.8	80.4	82
81	54.4	57.7	60.6	63.3	65.8	68.1	70.3	72.3	74.2	76.1	77.8	79.4	81
79	52.6	55.9	58.8	61.5	63.9	66.2	68.4	70.4	72.3	74.1	75.8	77.4	79
77	50.8	54	56.9	59.6	62.1	64.3	66.5	68.5	70.4	72.1	73.8	75.5	77
75	49.1	52.2	55.1	57.7	60.2	62.4	64.6	66.5	68.4	70.2	71.9	73.5	75
74	48.2	51.3	54.2	56.8	59.2	61.5	63.6	65.6	67.4	69.2	70.9	72.5	74
72	46.4	49.5	52.4	55	57.4	59.6	61.7	63.6	65.5	67.2	68.9	70.5	72
70	44.6	47.7	50.5	53.1	55.5	57.7	59.8	61.7	63.5	65.3	66.9	68.5	70
68	42.8	45.9	48.7	51.2	53.6	55.8	57.9	59.8	61.6	63.3	65	66.5	68
66	41	44.1	46.8	49.4	51.7	53.9	55.9	57.9	59.7	61.4	63	64.5	66
64	39.2	42.3	45	47.5	49.9	52	54	55.9	57.7	59.4	61	62.5	64
63	38.3	41.4	44.1	46.6	48.9	51.1	53.1	55	56.7	58.4	60	61.5	63
61	36.5	39.5	42.3	44.7	47	49.2	51.2	53	54.8	56.5	58	59.6	61
59	34.7	37.7	40.4	42.9	45.2	47.3	49.2	51.1	52.8	54.5	56.1	57.6	59
57	33	35.9	38.6	41	43.3	45.4	47.3	49.2	50.9	52.5	54.1	55.6	57

Very Uncomfortable	Uncomfortable	OK for most	Comfortable	Dry

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:

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

Where:

T_dew = 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:

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

T_dew ≈ 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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