Heat Index Calculator vs UV Exposure Calculator
Hot sunny days present two different outdoor hazards, and the site has a calculator for each. The heat index calculator answers “how hot does it actually feel?” using the official NWS procedure on air temperature and humidity. The UV exposure calculator answers “how much sun exposure am I planning for?” by combining the day’s UV index, minutes outdoors, and skin type. Both are summer planning tools built on official weather-health frameworks, but they measure different risks: heat stress versus ultraviolet radiation.
What each calculator does
The Heat Index Calculator takes air temperature and either relative humidity or dew point. It follows the NWS procedure exactly: it computes the simple formula, averages that result with air temperature, and — at 80°F or above — applies the nine-term Rothfusz regression, including the low-humidity (below 13%) and high-humidity (above 85%) adjustments within their temperature ranges. The result is the apparent temperature for shaded, light-wind conditions, rounded to the nearest whole degree Fahrenheit. In the article’s worked example, 90°F air at 60% humidity gives a heat index of about 100°F.
The UV Exposure Calculator takes the UV index, minutes outdoors, and Fitzpatrick skin type. It computes score = UV index × minutes × skin-type factor (2.0 for type I down to 0.5 for type VI), then classifies the score: below 50 low, 50–149 moderate, 150–299 high, and 300 and above very high. It also shows the official WHO/EPA UV index band for the entered value (0–2 low through 11+ extreme) with its protection actions. In the article’s worked example, UV index 6 for 30 minutes with type III skin scores 180 — High.
Side-by-side comparison
| Feature | Heat Index Calculator | UV Exposure Calculator |
|---|---|---|
| Question | How hot does it feel (heat stress)? | How much relative UV exposure is planned? |
| Inputs | Air temperature + relative humidity or dew point | UV index + minutes outdoors + Fitzpatrick skin type |
| Method | Official NWS procedure: simple formula, decision average, Rothfusz regression, adjustments | UV index × minutes × skin-type factor, then a score band |
| Output | Apparent temperature in °F, whole degrees | Relative score + low-to-very-high level + UV index band |
| Reference framework | NOAA/NWS heat index | WHO/EPA UV index scale and categories |
| Personalized risk? | No — no risk category or health interpretation | No — labeled heuristic, not a burn predictor |
When to use which
Use the heat index calculator when the question is about heat stress — planning outdoor work or exercise on a hot, humid day, or checking whether conditions push into the range where the NWS full regression and humidity adjustments apply. The page stays inside the official procedure’s branches and defers public guidance to NWS heat safety. It is the hot-weather counterpart of the wind chill calculator, which covers the cold side of apparent temperature.
Use the UV exposure calculator when the question is about sun exposure — comparing “30 minutes at UV index 6” against “60 minutes at UV index 3” before heading out, or checking how a skin-type factor changes the level. The score is explicitly a relative heuristic for comparing scenarios, not a measurement of UV dose and not a predictor of sunburn; use the day’s UV index and official sun safety guidance for protection decisions.
On many summer days you could reasonably reach for both — the heat index tells you how demanding the heat will be, and the UV score tells you how much sun you are signing up for. Neither page assigns a personalized limit, and both defer to official guidance for actual protection decisions.
Where to start
- Heat Index Calculator — NWS apparent temperature from temperature and humidity or dew point.
- UV Exposure Calculator — relative UV exposure score from UV index, minutes, and skin type.
Informational note: This page compares two weather-health planning tools and is not medical advice. Heat index values assume shaded, light-wind conditions, and the UV score is a labeled heuristic; follow current NWS heat safety and EPA/WHO sun safety guidance for real decisions.