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Calcimator

Heat Index Deep Calculator

Calculate the heat index using the full Rothfusz regression equation with NWS adjustments. Includes risk assessment and exposure-duration guidance.

Inputs

°F
%
hours

Results

Heat Index

117.6 °F

NWS Risk Level

Danger — Heat cramps/exhaustion likely, heatstroke possible

Heat Index47.6 °C
Feels Like Difference22.6 °F hotter
Exposure RiskHigh — Take frequent breaks in shade/AC
Recommended Water Intake2 liters
How to Use This Calculator
  1. Enter air temperature (°F) and relative humidity (%) for your location.
  2. Set exposure duration (hours) to assess cumulative heat stress risk.
  3. Review Heat Index (°F) — this is the apparent temperature felt by the body.
  4. Check NWS Risk Level and Exposure Risk to understand danger thresholds: above 103°F = danger, 125°F+ = extreme danger.
  5. Use Recommended Water Intake (liters) as a hydration planning guide for workers or athletes outdoors.

How the result changes with Air Temperature

Air TemperatureHeat IndexNWS Risk Level
7777.5 °FLow
95117.6 °FDanger — Heat cramps/exhaustion likely, heatstroke possible
116215.9 °FExtreme Danger — Heatstroke imminent
133337.2 °FExtreme Danger — Heatstroke imminent

What each input means

Air Temperature
Measured air temperature in degrees Fahrenheit. Heat index is most meaningful above 80°F.
Relative Humidity
Relative humidity as a percentage. Higher humidity reduces the body's ability to cool through evaporation.
Exposure Duration
Planned duration of outdoor exposure in hours. Longer exposure significantly increases heat illness risk.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    Air Temperature = 95, Relative Humidity = 65, Exposure Duration = 2 = 3 input(s) provided
  2. Calculate Heat Index
    117.6 = 117.6
  3. Calculate NWS Risk Level
    NWS Risk Level
    Danger — Heat cramps/exhaustion likely, heatstroke possible = Danger — Heat cramps/exhaustion likely, heatstroke possible
  4. Calculate Heat Index
    Heat Index
    47.6 = 47.6
  5. Calculate Feels Like Difference
    Feels Like Difference
    22.6 = 22.6

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