Dew Point
The honest measure of humidity
What is it?
The dew point is the temperature to which air must cool for its moisture to condense. Unlike relative humidity, it doesn't swing with temperature — making it the most reliable single number for how humid the air actually feels.
How we measure it
Computed from current temperature and relative humidity using the Magnus formula — a standard psychrometric conversion, labeled as computed.
Dew point comfort bands (NWS guide)
- < 10°CDryCrisp air; static and dry skin possible
- 10–16°CComfortablePleasant for almost everyone
- 16–18°CStickyNoticeably humid at exertion
- 18–21°CHumidUncomfortable; sweat evaporates slowly
- 21–24°CVery humidOppressive; exertion becomes stressful
- > 24°COppressiveDangerous with heat — cooling badly impaired
Within safe range
Below ~16°C dew point, sweat evaporates freely and the body cools itself efficiently at any reasonable temperature.
Beyond the range
Above ~21°C dew point, the air is so moist that sweating barely cools you — the same 32°C day feels brutal instead of warm, and heat illness risk climbs sharply. High dew points overnight also block the body's recovery from daytime heat.
Precautions
- Judge outdoor exertion by dew point, not relative humidity.
- Above 21°C dew point: slow your pace, hydrate more, rest in shade often.
- Combine with hot temperature = treat as heatwave conditions (see the Heatwave guide).
- Dehumidify indoor spaces; damp air also feeds mould and dust mites.