Bulb Score

Discover your local Wet Bulb Temperature normalized into an easy-to-understand 0-100 danger scale.

Analyzing local atmospheric conditions...

Use the icons in the top right to learn more about our methodology and the danger scale.

Bulb Score

--

Air Temp

--°F / --°C

Humidity

--%

Wet-Bulb

--°F / --°C

Location

Why This Exists

Traditional weather apps only show you air temperature and relative humidity. However, human survivability in extreme heat relies almost entirely on evaporative cooling (sweating).

When humidity is too high, sweat cannot evaporate. The body begins to absorb heat rather than shed it, leading to rapid, fatal heatstroke even in fully shaded environments.

How We Calculate It

This application calculates the Thermodynamic Wet-Bulb Temperature using Roland Stull's empirical formula, pulling real-time meteorological data for your specific location.

Because the raw scientific measurements of Wet-Bulb can be difficult for the general public to contextualize, we normalize the result into a 0 to 100 Bulb Score.

The Bulb Score

A score of 0 represents optimal biological cooling conditions. A score of 100 represents the theoretical absolute limit of human survivability (roughly 95°F at 100% humidity).

Beyond a score of 90, prolonged exposure will guarantee heatstroke in healthy adults, rendering fans and shade completely ineffective. Air conditioning or subterranean shelter becomes mandatory.

The scale is divided into 7 levels, mapping the wet bulb temperature into an easy-to-understand 0-100 score that grows more granular as conditions worsen.

0-49

Safe - Low Risk

Biological cooling functions optimally. Outdoor activities are perfectly safe for healthy individuals. Noticeable sweating may occur during vigorous exercise, but it cools the body efficiently.

Wet Bulb Range Under 77.0 °F (25.0 °C)

High Risk To None

Time to Overheat

Resting Safe

Light Exertion Safe

Heavy Exertion 2-4 Hours

50-69

Safe - With Caution

Generally safe for typical everyday activities. However, extenuating circumstances such as intense physical labor, heavy clothing, or underlying health conditions can induce heat stress. Hydration and breaks are recommended.

Wet Bulb Range 77.0 to 84.2 °F (25.0 to 29.0 °C)

High Risk To Vulnerable Groups

Time to Overheat

Resting Safe

Light Exertion 2-4 Hours

Heavy Exertion 45-60 Mins

70-79

Danger

Dangerous conditions. Severe stress on the cardiovascular system. Unacclimatized workers should limit physical labor. The body struggles significantly to maintain core temperature.

Wet Bulb Range 84.2 to 87.8 °F (29.0 to 31.0 °C)

High Risk To Everyone

Time to Overheat

Resting >6 Hours

Light Exertion 1-1.5 Hours

Heavy Exertion 30-45 Mins

80-89

Extreme Danger

Extremely dangerous conditions. Sweating becomes highly ineffective at shedding heat. Core body temperature will rise rapidly during typical activities. Outdoor exposure must be strictly limited and indoor AC or subterranean shelter is mandatory.

Wet Bulb Range 87.8 to 91.4 °F (31.0 to 33.0 °C)

High Risk To Everyone

Time to Overheat

Resting 4-6 Hours

Light Exertion 30-45 Mins

Heavy Exertion 15-25 Mins

90-100

Imminent Lethality

Imminent lethality. Complete physiological failure. Human survivability is impossible beyond a very short duration, even if resting, fully shaded, and fully hydrated. Indoor AC is mandatory.

Wet Bulb Range 91.4+ °F (33.0+ °C)

High Risk To Everyone

Time to Overheat

Resting <1 Hour

Light Exertion <5 Mins

Heavy Exertion Immediate