The dew point is the temperature at which air becomes saturated and water starts to condense. Calculate it from the air temperature and relative humidity, or work backwards to the humidity from a dew point, and see how comfortable the air feels.
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How to use the Dew Point Calculator
Choose what to calculate: dew point, relative humidity or air temperature.
Pick °C or °F; the dew point uses the same unit as the temperature.
Enter the two known values, for example 25 °C and 60% humidity.
Press Calculate to see the result, the comfort level and the working.
Use the table to see the dew point at other humidity levels for the same temperature.
Dew point table (°C)
Air temp ↓ / RH →
20%
30%
40%
50%
60%
70%
80%
90%
0 °C (32 °F)
-20.3
-15.5
-12.0
-9.2
-6.8
-4.8
-3.0
-1.4
10 °C (50 °F)
-12.0
-6.8
-3.0
0.0
2.6
4.8
6.7
8.4
15 °C (59 °F)
-7.8
-2.4
1.5
4.7
7.3
9.6
11.6
13.4
20 °C (68 °F)
-3.7
1.9
6.0
9.3
12.0
14.4
16.4
18.3
25 °C (77 °F)
0.5
6.2
10.5
13.9
16.7
19.1
21.3
23.2
30 °C (86 °F)
4.6
10.5
14.9
18.4
21.4
23.9
26.2
28.2
35 °C (95 °F)
8.7
14.8
19.4
23.0
26.1
28.7
31.0
33.1
Read across from the air temperature to the humidity column. Values use the Magnus formula above.
Dew point comfort scale
Dew point
How it feels
Below 10 °C (50 °F)
Dry, very comfortable
10–13 °C (50–55 °F)
Comfortable
13–16 °C (55–60 °F)
Slightly humid, noticeable
16–18 °C (60–65 °F)
Sticky
18–21 °C (65–70 °F)
Humid, uncomfortable
21–24 °C (70–75 °F)
Very humid, oppressive
Above 24 °C (75 °F)
Extremely oppressive
Relative humidity tells you how close the air is to saturation at its current temperature, so it drops as the afternoon warms up even when the amount of moisture is unchanged. The dew point measures the moisture itself, which is why forecasters use it to describe how muggy a day will feel.
Frequently asked questions
How do you calculate the dew point?
With the Magnus formula: γ = ln(RH/100) + a·T/(b + T), then Td = b·γ/(a − γ), where T is the temperature in °C, RH the relative humidity in %, a = 17.625 and b = 243.04 °C. At 25 °C and 60% humidity the dew point is about 16.7 °C.
How do you get relative humidity from the dew point?
RH = 100 × e^(a·Td/(b + Td)) ÷ e^(a·T/(b + T)) with the same constants. For example air at 30 °C with a 20 °C dew point has a relative humidity of about 55%.
What dew point is comfortable?
Most people feel comfortable with a dew point below about 13 °C (55 °F). From 16 °C (60 °F) the air feels sticky, above 18 °C (65 °F) humid and uncomfortable, and above 21 °C (70 °F) oppressive. Unlike relative humidity, the dew point does not change as the air warms during the day, so it is a better measure of mugginess.
How accurate is the Magnus formula?
With the Alduchov and Eskridge (1996) constants it is accurate to within about 0.35 °C for temperatures from −45 °C to 60 °C, which is better than most household hygrometers.
What does the dew point spread tell me?
The difference between air temperature and dew point. When it is under about 2–3 °C, fog, dew or frost is likely, especially overnight. For convective clouds the cloud base is roughly 125 m (about 400 ft) higher for every 1 °C of spread.
Why does condensation form on windows and cold drinks?
Any surface colder than the dew point cools the air touching it below saturation, so water condenses. Keeping indoor dew point low (by ventilating or dehumidifying) or keeping surfaces warmer prevents condensation and mould.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.