Humidex Calculator (Canadian Feels-Like)

Three ways: input (dew point vs relative humidity), model (pure vapor-pressure arithmetic vs Steadman's physiological simulation of a walking human), and calibration (humidex reads numerically higher — 30°C at 22°C dew point gives humidex 40 but heat index ~37°C/98°F). Neither is 'wrong'; they're different instruments. Compare each only against its own advisory bands: Environment Canada flags 40+ as great discomfort, 45+ as dangerous.

Because dew point is the absolute-moisture number: RH swings all day as temperature changes even when the air's actual water content is constant, while dew point sits still. A formula built on vapor pressure (computed from dew point) tracks the physical quantity that loads your sweating — and lets the same observation work morning and afternoon. Meteorologists generally regard dew point as the honest mugginess metric for exactly this reason.

Southern Ontario and Quebec see 35–40 routinely in July heat waves and 40–45 in the bad ones; the record zone is 45–50 (Windsor and Ottawa valley readings near 50 are infamous). Prairie heat tends dry — high temperature, modest humidex gap — while Great Lakes humidity drives the spread. Above 40, Environment Canada issues heat warnings in combination with temperature criteria that vary by region.

The folk scale meteorologists quote: below 10°C dew point, crisp; 10–15 comfortable; 16–18 noticeable; 18–21 humid and sticky; above 21°C oppressive — and above 24, tropical-storm air. The humidex formula encodes this smoothly: each degree of dew point above ~7°C adds roughly 0.6–1 humidex point at summer temperatures. Our dew-point calculator converts any T/RH pair into this more honest currency.