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Dew Point Calculator

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The dew point is the temperature at which air becomes saturated and water vapour starts to condense. Unlike relative humidity, it tells you how muggy the air actually feels: a 20°C dew point is sticky no matter the air temperature. Enter the current temperature and relative humidity below and this calculator returns the dew point in both °C and °F instantly, using the well-established Magnus approximation that weather services rely on every day.

How to find the dew point

  1. 1

    Enter the air temperature

    Type the current temperature in degrees Celsius.

  2. 2

    Enter the relative humidity

    Add the relative humidity as a percentage from 0 to 100.

  3. 3

    Read the dew point

    The result appears instantly in °C and °F, ready to copy.

The Magnus formula

The dew point is estimated from temperature and relative humidity with the Magnus-Tetens approximation:

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

Where T is the air temperature in °C, RH is the relative humidity in percent, and the constants are a = 17.27 and b = 237.7 °C. The result Td is the dew point in °C; multiply by 9/5 and add 32 for °F. This approximation is accurate to roughly ±0.4 °C for temperatures between 0 °C and 60 °C and humidity above about 1%.

Worked example

Take T = 25 °C and RH = 60%:

  • α = (17.27 × 25) / (237.7 + 25) + ln(0.60) = 1.6433 + (−0.5108) = 1.1325
  • Td = (237.7 × 1.1325) / (17.27 − 1.1325) = 269.2 / 16.137 ≈ 16.7 °C (≈ 62.1 °F)

So air at 25 °C and 60% humidity has a dew point near 16.7 °C, comfortable, but on the humid side.

Dew point comfort guide

Dew point (°C) Dew point (°F) How it feels
< 10 < 50 Dry, crisp
10 – 15 50 – 59 Pleasant
16 – 18 60 – 65 Slightly humid
19 – 21 66 – 70 Humid, sticky
22 – 24 71 – 75 Oppressive
≥ 24 ≥ 75 Miserable, tropical

Pitfalls to avoid

  • Dew point never exceeds air temperature. At 100% humidity the two are equal; if your inputs give a dew point above the temperature, the humidity value is wrong.
  • Relative humidity alone is misleading. 90% RH on a cold morning is far drier than 60% RH on a hot afternoon, compare dew points, not RH.
  • Very low humidity. The formula assumes RH ≥ 1%; this tool clamps the input to a 1% floor so the logarithm stays defined.

Frequently Asked Questions

Relative humidity is the percentage of moisture the air holds relative to its maximum at the current temperature, so it changes as the temperature changes. The dew point is an absolute measure of moisture content: it is the temperature at which the air would have to cool to reach saturation. A higher dew point always means more water vapour in the air.

When the dew point is high, the air is already near saturation, so sweat evaporates slowly and your body struggles to cool itself. Dew points above 21°C (70°F) feel sticky, and above 24°C (75°F) most people find the air oppressive regardless of the actual temperature.

The Magnus-Tetens approximation used here is accurate to about ±0.4°C for temperatures between 0°C and 60°C and humidity above roughly 1%. That is well within the precision of typical home thermometers and hygrometers, and it is the same method many weather services use.

The temperature and humidity you enter are sent to our server only to compute the dew point. Your values are not stored or shared, and there are no accounts.

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