A familiar situation
Schätzen Sie, wie heiß sich feuchte Sommerluft im Schatten anfühlt.
How to use this calculator
- Enter air temperature, relative humidity.
- Select Calculate to see the answer and its breakdown.
- Keep a scenario, change an input and compare the results.
Use consistent units and check the assumptions below before applying the result.
How heat index is calculated
Estimate apparent heat using the National Weather Service Rothfusz regression for warm, humid conditions, with its low-humidity and high-humidity adjustments. It is intended for shaded conditions and can be misleading outside its calibrated range; direct sun and exertion increase heat stress. At 90°F and 70% relative humidity, the index is approximately 106°F. The calculation validates each input and keeps its stated units explicit. No. The standard index assumes shade; sun can raise apparent heat and risk. This is an estimate for the stated assumptions; confirm measurements and any applicable professional or local standards before relying on it.
Rothfusz regression with NWS humidity adjustmentsAt 90°F and 70% relative humidity, the index is approximately 106°F.
Assumptions & useful context
NWS approximation for shade; use local heat-safety guidance.
Frequently asked questions
Does the result include direct sunlight?
No. The standard index assumes shade; sun can raise apparent heat and risk.
Is the equation valid at all temperatures?
No. NWS guidance uses a simpler approach below about 80°F and warns about extreme conditions.