Calculator Tools
Dew Point Calculator
Calculate the dew point from air temperature and relative humidity using the Magnus-Tetens formula. Comfort bands, spread, and a reference chart.
Temperature units
Relative humidity should be measured at the same air temperature you entered above. Most thermo-hygrometers and weather forecasts report this directly.
Dew point
64.9 °F
Equivalent to 18.3 °C
Slightly sticky
Mugginess becomes obvious. Sweat evaporates slowly; outdoor exertion is noticeably harder. Sleep quality may drop without air movement.
Comfort range: dew point 18 to 21 C
- Air temperature
- 80.0 °F
- Relative humidity
- 60.0 %
- Dew point spread
- 15.1 °F
- Absolute humidity
- 15.13 g/m³
26.7 °C
Moisture saturation of the air at the current air temperature.
How much you would need to cool the air to reach saturation.
Grams of water vapour per cubic metre of air.
Dew point reference chart
Read a cell to see the dew point for a given air temperature row and relative humidity column. Cells are colour-coded by comfort band.
Values shown in Fahrenheit.
| Air temp | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% | 100% |
|---|---|---|---|---|---|---|---|---|---|---|
| 110 °F | 41 | 60 | 72 | 80 | 87 | 93 | 98 | 102 | 106 | 110 |
| 100 °F | 34 | 52 | 63 | 71 | 78 | 84 | 88 | 93 | 97 | 100 |
| 90 °F | 26 | 44 | 54 | 62 | 69 | 74 | 79 | 83 | 87 | 90 |
| 80 °F | 19 | 35 | 46 | 54 | 60 | 65 | 69 | 73 | 77 | 80 |
| 70 °F | 11 | 27 | 37 | 45 | 51 | 55 | 60 | 64 | 67 | 70 |
| 60 °F | 3 | 19 | 28 | 36 | 41 | 46 | 50 | 54 | 57 | 60 |
| 50 °F | -5 | 10 | 20 | 27 | 32 | 37 | 41 | 44 | 47 | 50 |
| 40 °F | -12 | 2 | 11 | 18 | 23 | 27 | 31 | 34 | 37 | 40 |
| 30 °F | -20 | -6 | 2 | 9 | 14 | 18 | 21 | 25 | 27 | 30 |
- Dry and comfortable
- Very comfortable
- Comfortable for most
- Slightly sticky
- Oppressive
- Severely oppressive
What this tool covers
- Magnus-Tetens formula: uses the Sonntag 1990 coefficients (a = 17.625, b = 243.04 °C), the standard meteorological approximation. Quoted worst-case error is about 0.4 °C across -40 °C to +50 °C.
- Comfort bands: the tool labels the result as dry, comfortable, sticky, oppressive, or severely oppressive using the dew-point bands the National Weather Service uses to describe summer mugginess.
- Spread: shows the gap between air temperature and dew point. A near-zero spread means fog, dew, or condensation is likely; a wide spread means crisp, dry air.
- Absolute humidity: reports g/m³ of water vapour for HVAC, grow rooms, herpetology tanks, and condensation control where dew point alone is not enough.
- Frost point note: when the result falls below 0 °C the tool labels it as the frost point so you know the saturation curve assumed water rather than ice.
- Local only: nothing you type is uploaded. The math runs entirely in your browser.
How to use
- Pick Fahrenheit or Celsius, then enter the current air temperature.
- Enter the relative humidity in percent, or tap one of the quick chips (20%, 30%, ..., 90%) to try a scenario.
- Read the dew point in both unit systems, the spread, absolute humidity, and the comfort band; use Copy report to grab a plain-text summary.
- Scroll down to the reference chart to scan dew point across the full temperature and humidity grid.
About this tool
Dew Point Calculator returns the temperature at which the air you describe would have to be cooled, at constant pressure, to reach saturation. Enter an air temperature in Fahrenheit or Celsius and a relative humidity between 0 and 100 percent; the tool reports the dew point in both unit systems, the spread below the air temperature, the absolute humidity in g/m³, and a comfort band sourced from National Weather Service summary language (dry, very comfortable, comfortable, slightly sticky, oppressive, or severely oppressive). The math uses the Magnus-Tetens formulation with Sonntag's 1990 coefficients, the same approximation cited by meteorological agencies and most HVAC references, with a published worst-case error of about 0.4 °C across realistic atmospheric ranges. When the result falls below 0 °C the tool labels it as the frost point so you know the saturation curve assumed water rather than ice. Useful for judging summer mugginess at a glance, deciding whether your bedroom needs a dehumidifier, sizing condensation risk on cold-water pipes or single-pane windows, briefing outdoor workers ahead of a humid shift, troubleshooting fogged camera lenses or grow tents, and answering questions like what is the dew point at 80 °F and 60 percent humidity. A built-in NWS-style reference chart spans 30 °F to 110 °F across 10 to 100 percent relative humidity, colour-coded by comfort band, for sanity checks and planning. Pair it with the heat-index calculator for warm-weather feels-like temperatures and the wind-chill calculator for the cold side. Every conversion and classification runs locally in your browser; the values you type are never uploaded to a server.
Free to use. Works in your browser. No signup, no login.
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