Heat Index at 95°F, 80% humidity
What 95°F, 80% humidity actually feels like, using the official NWS heat index formula. Adjust either value below to try your own numbers.
Feels Like
-115149°F
Little to no heat-related risk from normal activity.
At 95°F with 80% relative humidity, it feels like -115149°F — about 0° hotter than the actual air temperature.
Actual Temperature
95°F
Feels-Like Rise
+0°
What is a Heat Index Calculator?
A heat index calculator estimates how hot the air actually feels to the human body, combining air temperature with relative humidity. High humidity slows the evaporation of sweat off your skin — and evaporation is the body's primary cooling mechanism — so humid heat feels significantly more oppressive than dry heat at the exact same thermometer reading.
This calculator uses the Rothfusz regression, the formula developed by the National Weather Service and used in official US heat advisories. It's most accurate at temperatures of 80°F or higher with relative humidity of 40% or more, which is why the formula switches to a simpler estimate outside that range.
The Rothfusz Regression Formula
Where T is air temperature in °F and RH is relative humidity as a percentage. This full regression only applies when the simplified estimate — an easier formula averaging temperature and humidity effects — would already suggest a heat index of 80°F or higher. Below that, the simplified estimate is used directly since the full regression isn't calibrated for milder conditions. Two further corrections apply at the extremes: a downward adjustment for low humidity (below 13%) at high temperatures, where dry heat feels somewhat less oppressive, and an upward adjustment for very high humidity (above 85%) at moderate temperatures.
Why Humidity Matters So Much
Sweat cools the body by evaporating, which carries heat away as it changes from liquid to vapor. High relative humidity means the surrounding air is already close to saturated with water vapor, so sweat evaporates much more slowly — the cooling mechanism becomes far less effective right when the body needs it most. This is why 90°F at 70% humidity can feel considerably hotter and more dangerous than 90°F at 20% humidity, even though the thermometer reads identically in both cases.
Heat Index vs. Wind Chill
Heat index and wind chill are conceptual opposites: both estimate a "feels like" temperature, but heat index accounts for humidity's effect on hot weather, while wind chill accounts for wind's effect on cold weather. Sunshine can add up to about 15°F to the effective heat index beyond what the shaded-air formula calculates, which is why official heat advisories often note that direct sun exposure makes conditions feel even worse than the reported number.
Example — Your Current Inputs
At 95°F with 80% relative humidity, it feels like -115149°F — about 0° hotter than the actual air temperature.
Additional Example — A Humid Summer Day
On a day with an actual temperature of 83°F and 70% relative humidity, the heat index works out to about 88°F — five degrees hotter than the thermometer reading, and enough to push conditions from "comfortable" into the "caution" category where prolonged outdoor activity can cause fatigue.
About These Parameters
- Air Temperature
- The actual shaded-air thermometer reading, in °F. Direct sunlight can make conditions feel meaningfully hotter than this number alone suggests.
- Relative Humidity
- The percentage of moisture in the air relative to the maximum the air could hold at that temperature. Higher values mean sweat evaporates more slowly, making heat feel more intense and dangerous.
Frequently Asked Questions
Does the heat index account for direct sunlight or wind?
No — the standard heat index formula assumes shaded conditions with light wind. Full sun exposure can add up to roughly 15°F to how hot conditions actually feel, which is why official heat advisories often warn that reported heat index values understate the risk for anyone working or exercising directly in the sun.
At what heat index should I be concerned?
The National Weather Service considers a heat index of 90°F or higher "extreme caution" territory, where heat cramps and heat exhaustion become likely with continued exposure or physical activity. At 105°F and above, heat stroke becomes a real possibility, and above 130°F, heat stroke is highly likely — this is emergency territory that calls for staying indoors in air conditioning.
Why does the formula change at low temperatures or low humidity?
The full Rothfusz regression was fit to data collected at higher temperatures and humidity, so it isn't reliable outside that range. Below the point where a simpler estimate would suggest less than 80°F, the calculator uses that simpler formula directly instead, since the full regression can actually produce inaccurate results in milder conditions.