★ EVERYDAY · WEATHER · HUMIDITY
At 75 °F and 60% humidity the dew point is 60.16 °F — muggy air that only has to cool 14.84 degrees before dew forms. Put in the air temperature and the relative humidity and the calculator works out the dew point in °F and °C, the temperature–dew-point spread, and how the air feels. This one is the DEW POINT tool — temperature and humidity in, dew point out — the heat-index-calculator page is the FEELS-LIKE tool — how hot humid air feels on skin — not the condensation temperature; the wind-chill-calculator page is the COLD FEELS-LIKE tool — how cold wind makes it feel — not humidity; and the celsius-to-fahrenheit-chart page is the CONVERSION CHART — temperatures between °C and °F — not a dew-point calculation. No dew-point calculator exists on this site — this one is the first.
The dew point is the temperature the air must cool to before water vapour starts condensing — the temperature at which dew forms. On the defaults it is 60.16 °F: at 75 °F and 60% humidity, the air would have to cool 14.84 degrees. The Magnus formula gives it to about ±0.5 °C in the usual weather range, and below freezing this is the dew point, not the frost point.
It means the air at 75 °F and 60% humidity holds enough water vapour that it only has to cool to 60.16 °F before the vapour starts condensing — that is the dew point, and the gap between the air and the dew point, the spread, is 14.84 °F. A narrow spread means the air is close to saturation: at 85 °F and 90% humidity the spread is only 3.27 degrees, and dew is minutes away. A wide spread means dry air: at 90 °F and 40% humidity the spread is 27.61 degrees, and nothing will condense until the night cools a long way. On the headline numbers the air feels muggy, because a dew point between 60 °F and 65 °F is the muggy band.
The Magnus formula is an approximation. It is accurate to about ±0.5 °C in the usual weather range, which is closer than most home hygrometers measure humidity in the first place. Your humidity reading is the weak link: a sensor that reads 5% high moves the dew point by about a degree. Treat the answer as good to about a degree, not to the second decimal.
Below freezing it is the dew point, not the frost point. Under 32 °F the water in the air deposits as frost, not dew, and the frost point sits a little higher than the dew point the formula gives — at 0 °F and 50% humidity the formula says −14.17 °F, and the frost point is a degree or two above that. Do not use the number below freezing as a frost forecast without the correction.
At 100% humidity the dew point is the air temperature. Saturated air cannot hold more vapour, so the dew point equals the temperature and the spread is zero — that is fog, or rain, or dew forming right now. At 0% there is no vapour at all, so there is no dew point to calculate, and the calculator says so rather than dividing by zero.
On the defaults: 75 °F, 60% relative humidity.
The defaults are a warm afternoon, 75 °F and 60% humidity — a typical muggy summer day. They are a starting point, not a forecast: your temperature and humidity are the numbers that matter, and the calculator works in Fahrenheit or Celsius. The Magnus formula uses a = 17.27 and b = 237.7 °C, and it is accurate to about ±0.5 °C in the usual weather range. Below freezing the frost point differs slightly from the dew point given here. Put your numbers in, read the answer, and check the working before you use it.
These notes repeat in every explainer section because this page is built to be read start to finish: the Magnus formula is an approximation; below freezing it is the dew point, not the frost point; and at 100% humidity the dew point is the air temperature.
| Output | Formula | What it means |
|---|---|---|
| Temperature | input | 75 °F. |
| Relative humidity | input | 60%. |
| Dew point | Magnus formula | 60.16 °F. |
| Dew point | Magnus formula | 15.64 °C. |
| Temperature–dew-point spread | air temperature − dew point | 14.84 °F. |
| Comfort | dew-point bands | muggy. |
| Verdict | in words | At 75 °F and 60% humidity the dew point is about 60.16 °F. |
| Reverse: Smallest whole RH% for a dew point of 60 °F or more at 75 °F | step | 60%: Dew point 60.16 °F (15.64 °C), spread 14.84 °F — muggy. |
| Reverse: Largest whole RH% for a dew point of 55 °F or less at 75 °F | step | 49%: Dew point 54.53 °F (12.51 °C), spread 20.47 °F — comfortable. |
| Reverse: Smallest whole RH% for a dew point of 70 °F or more at 90 °F | step | 53%: Dew point 70.53 °F (21.41 °C), spread 19.47 °F — oppressive. |
| Reverse: Smallest whole RH% for a dew point of 32 °F or more at 50 °F | step | 50%: Dew point 32.10 °F (0.06 °C), spread 17.90 °F — comfortable. |
| Reverse: Largest whole RH% for a dew point of 40 °F or less at 70 °F | step | 33%: Dew point 39.56 °F (4.20 °C), spread 30.44 °F — comfortable. |
| Reverse: Smallest whole RH% for a dew point of 50 °F or more at 80 °F | step | 36%: Dew point 50.62 °F (10.35 °C), spread 29.38 °F — comfortable. |
| 75 °F, 60% RH | same model | Dew point 60.16 °F (15.64 °C), spread 14.84 °F — muggy. |
| 90 °F, 40% RH | same model | Dew point 62.39 °F (16.88 °C), spread 27.61 °F — muggy. |
| 32 °F, 100% RH | same model | Dew point 32.00 °F (0.00 °C), spread 0.00 °F — comfortable. |
| 70 °F, 50% RH | same model | Dew point 50.49 °F (10.27 °C), spread 19.51 °F — comfortable. |
| 100 °F, 80% RH | same model | Dew point 92.68 °F (33.71 °C), spread 7.32 °F — oppressive. |
| 50 °F, 30% RH | same model | Dew point 19.80 °F (−6.78 °C), spread 30.20 °F — comfortable. |
| 25 °C, 60% RH | same model | Dew point 62.03 °F (16.68 °C), spread 14.97 °F — muggy. |
| 20 °C, 80% RH | same model | Dew point 61.59 °F (16.44 °C), spread 6.41 °F — muggy. |
| 0 °F, 50% RH | same model | Dew point −14.17 °F (−25.65 °C), spread 14.17 °F — comfortable. |
| 85 °F, 90% RH | same model | Dew point 81.73 °F (27.63 °C), spread 3.27 °F — oppressive. |
| RH 100% at 75 °F | same model | Dew point 75.00 °F (23.89 °C), spread 0.00 °F — oppressive. |
| RH 0% at 75 °F | same model | Relative humidity must be more than 0% — at 0% there is no water vapour to condense.. |
| RH 101% at 75 °F | same model | Relative humidity cannot be more than 100%.. |
| −10 °F, 60% RH (below freezing) | same model | Dew point −20.03 °F (−28.90 °C), spread 10.03 °F — comfortable. |
| Non-numeric temperature | same model | Enter numbers for every field.. |
| RH 99% at 70 °F | same model | Dew point 69.70 °F (20.95 °C), spread 0.30 °F — oppressive. |
| 120 °F, 10% RH (hot and dry) | same model | Dew point 48.56 °F (9.20 °C), spread 71.44 °F — comfortable. |
| 32 °F, 50% RH | same model | Dew point 15.49 °F (−9.17 °C), spread 16.51 °F — comfortable. |
| RH −5% at 75 °F | same model | Relative humidity must be more than 0% — at 0% there is no water vapour to condense.. |
| 68 °F, 65% RH | same model | Dew point 55.79 °F (13.21 °C), spread 12.21 °F — slightly sticky. |
| 25 °C, 100% RH | same model | Dew point 77.00 °F (25.00 °C), spread 0.00 °F — oppressive. |
The arithmetic is exact on the numbers you type: 75 °F and 60% humidity give a dew point of 60.16 °F by the Magnus formula. What the calculator cannot do is measure your air: the Magnus approximation is accurate to about ±0.5 °C in the usual weather range, and a humidity sensor that reads a few percent off moves the dew point by about a degree. Below freezing the frost point differs slightly from the dew point given here — the formula gives the dew point, not the frost point. The comfort bands are the standard ones: under 55 °F comfortable, 55–60 slightly sticky, 60–65 muggy, 65+ oppressive. Treat the answer as good to about a degree, not to the second decimal.
At 75 °F and 60% humidity the dew point is about 60.16 °F — the air would have to cool 14.84 degrees before dew forms. 90 °F and 40% humidity: dew point 62.39 °F. 32 °F and 100% humidity: dew point 32 °F exactly. Smallest whole RH% for a dew point of 60 °F or more at 75 °F: 60%. Largest whole RH% for a dew point of 55 °F or less at 75 °F: 49%. Smallest whole RH% for a dew point of 70 °F or more at 90 °F: 53%. Smallest whole RH% for a dew point of 32 °F or more at 50 °F: 50%. Largest whole RH% for a dew point of 40 °F or less at 70 °F: 33%. Smallest whole RH% for a dew point of 50 °F or more at 80 °F: 36%. Source: Bright Side Kit, brightoolbox.com.
The dew point is the temperature the air must cool to before water vapour starts condensing into dew. At 75 °F and 60% humidity the dew point is 60.16 °F — cool the air 14.84 degrees and dew forms.
With the Magnus formula: α = 17.27 × T / (237.7 + T) + ln(RH / 100), then Td = 237.7 × α / (17.27 − α), with T in Celsius. The worked example above runs it step by step for 75 °F and 60% humidity.
Under 55 °F feels comfortable; 55–60 °F is slightly sticky; 60–65 °F is muggy; 65 °F and over is oppressive. At 60.16 °F the headline air is muggy — sweat dries slowly and the air feels heavy.
Exactly the air temperature — the spread is zero. At 32 °F and 100% humidity the dew point is 32 °F: the air is saturated, and dew or fog is forming right now.
Because there is no water vapour in the air to condense. The formula needs ln(RH / 100), and ln(0) is undefined, so the calculator refuses 0% rather than inventing a number.
Relative humidity is how full the air is, as a percentage; the dew point is the temperature at which it would be full. 60% humidity at 75 °F means a dew point of 60.16 °F; the same 60% at 90 °F means a dew point of 62.39 °F — warmer air holds more vapour.
No — below freezing they differ slightly. The Magnus formula gives the dew point; the frost point, where vapour deposits as frost, sits a little higher. At 0 °F and 50% humidity the dew point is −14.17 °F, and the frost point is a degree or two above that.
The air is close to saturation — dew, fog or rain is near. At 85 °F and 90% humidity the spread is only 3.27 degrees; at 90 °F and 40% humidity it is 27.61 degrees, and the air is dry.