Dew Point Calculator
Enter air temperature and relative humidity to get dew point, wet bulb and a straight comfort read — dew point, not RH, is the real comfort metric.
Open calculatorLast updated: 2026-09-15
How the calculation works
- The Magnus-Tetens formula inverts the vapor-pressure relation: dew point is where the current moisture content becomes saturated.
- The wet-bulb approximation (Stull) gives the temperature of evaporative cooling — the physical limit of swamp coolers and the metric for heat stress.
- Comfort bands come from empirical dew-point comfort research, not the humidity percentage.
Worked example
Interpreting the result
Dew point is the amount of moisture in the air, expressed as a temperature — it doesn't change with air temperature the way RH does. Air conditioning works largely by cooling air below its dew point and wringing water out. Surfaces (cold pipes, single-pane windows) at or below dew point will condense water — that's the number for mold prevention.
Assumptions
- Standard atmospheric pressure near sea level; the Magnus approximation shifts slightly at altitude.
- Ranges: −40 to 50 °C input, ±0.35 °C accuracy.
Limitations
- Does not replace full psychrometric charts when precise enthalpy or humidity ratio is needed.
- Wet bulb is an approximation (Stull), accurate within ~1 °C for normal conditions.
Dew point (°C) by air temperature and relative humidity
| Air temperature | 40 % RH | 50 % RH | 60 % RH | 70 % RH | 80 % RH |
|---|---|---|---|---|---|
| 20 °C | 6.0 | 9.3 | 12.0 | 14.4 | 16.4 |
| 22 °C | 7.8 | 11.1 | 13.9 | 16.3 | 18.4 |
| 24 °C | 9.6 | 12.9 | 15.8 | 18.2 | 20.3 |
| 26 °C | 11.4 | 14.8 | 17.6 | 20.1 | 22.3 |
| 28 °C | 13.1 | 16.6 | 19.5 | 22.0 | 24.2 |
| 30 °C | 14.9 | 18.4 | 21.4 | 23.9 | 26.2 |
| 32 °C | 16.7 | 20.3 | 23.3 | 25.8 | 28.1 |
Dew point and relative humidity are different things
Relative humidity says how full the air is compared with what it could hold at its current temperature, so it changes when the temperature changes. Dew point is the temperature at which the air would be completely full, and it only changes when the amount of moisture changes. That makes it the better figure for judging condensation.
Worked scenario: warm room, cold pipe
Air at 25 °C and 60 % relative humidity has a dew point of 16.7 °C (62 °F). Any surface colder than that will collect condensation, so a cold-water pipe at 15 °C running through this room will sweat unless it is insulated.
Where it matters
- Cold water pipes, ducts and windows: insulate or raise the surface temperature above the dew point.
- Air conditioning: the coil removes moisture because it runs below the dew point of the room air.
- Comfort: many people find air with a dew point above roughly 16–18 °C humid.
Frequently asked questions
What dew point is uncomfortable?
Above 60 °F (15.5 °C) feels muggy to most people; above 70 °F (21 °C) is oppressive. Below 55 °F (13 °C) feels crisp and dry.
Why does dew point matter more than humidity %?
RH changes with temperature even when moisture content is constant — 50% RH at 30 °C is far more humid air than 50% RH at 15 °C. Dew point measures the actual water content.