Steadman apparent temperature calculator with wind and radiation

Unlike a conventional heat index, this calculation can represent the cooling effect of wind and the added load from absorbed radiation. Enter temperature in degrees Celsius, relative humidity from zero to one hundred percent, wind speed in metres per second, and optional net radiation in watts per square metre. The result includes the apparent temperature, calculated vapour pressure, and each individual contribution for a transparent, reproducible assessment.

Choose measurements that describe the same exposure

Apparent temperature is most useful when all inputs represent the conditions experienced by the same person, place, and moment. Enter air temperature in degrees Celsius and relative humidity as a percentage, not a fraction. Wind speed should describe airflow at the exposed person rather than a distant weather station if local shelter, machinery, or building geometry changes it. Net radiation is the absorbed radiant heat per square metre after incoming and outgoing effects are combined. Set it to zero when you want the commonly used shaded version or when no defensible radiation measurement exists. A positive value represents net radiant gain, such as exposure to sun or a hot surface, while a negative value represents net radiant loss. Do not substitute solar irradiance directly unless it has already been converted to the net radiation absorbed by the subject. Keeping the measurements consistent matters more than adding a highly uncertain radiation estimate, because the calculator faithfully applies whatever values it receives.

Understand how the Steadman equation builds the result

The calculation first converts temperature and relative humidity into water-vapour pressure using a saturation-vapour-pressure approximation. That pressure drives the positive evaporation-related term in the Steadman expression: humid air generally reduces the body's opportunity to shed heat through evaporation, so its apparent-temperature contribution rises. Wind contributes a negative term proportional to speed, representing convective cooling. Radiation contributes through a term divided by wind speed plus ten, so the same radiant load has a smaller temperature effect as airflow increases. Finally, the equation combines these contributions with air temperature and a fixed calibration offset. The response exposes vapour pressure and all three contributions alongside the final apparent temperature. These fields make comparisons easier: users can hold temperature constant, vary one environmental input, and see exactly which part moved. Rounding happens only for the reported fields; the formula uses full floating-point precision internally before producing the selected number of decimal places.

Interpret the estimate with appropriate caution

Use the result as an environmental indicator, not as a personal medical threshold. Steadman's apparent temperature represents a standardized heat-balance relationship and cannot account for every person's clothing, work rate, hydration, acclimatization, age, health, or access to shade. It is valuable for comparing scenarios, enriching weather observations, screening outdoor plans, and documenting how wind or radiant exposure changes a baseline condition. For operational heat safety, combine it with the rules, measurements, and exposure limits required by the relevant workplace or public-health authority. Relative humidity must remain between zero and one hundred percent; values outside that physical percentage range cause an error rather than being silently corrected. Negative wind speed is also invalid. When radiation is unknown, report that the zero-radiation shaded form was used so readers do not mistake the result for a full-sun estimate. Automated users can call the API for $0.002 per request, while browser calculations use the same deterministic formula without sending the calculation elsewhere.