The thermometer only
tells you half of it.
WetBulbTracker shows the real heat stress your body faces — the validated standard the pros rely on, made personal and hyper-local. Free, anywhere on Earth.
Your thermometer doesn’t tell you the whole story.
Air temperature ignores the one thing that decides whether heat is dangerous: whether your sweat can still cool you. When humidity climbs, evaporation stalls — and the same 95° can be a pleasant dry afternoon or a serious health risk.
That’s heat stress— and wet-bulb globe temperature (WBGT) measures it, capturing heat, humidity, wind, and the sun beating down in one honest number. It’s the standard the military, athletic associations, and occupational safety boards rely on to decide when it’s no longer safe to be out. It’s the number we put front and center.
Our name comes from heat science’s most extreme line: at a wet-bulb temperature near 35°C (95°F), even a healthy person at rest in the shade can no longer cool down. You’ll rarely be near that limit — but the same physics drives everyday heat stress, and that’s the danger we put in your hand, wherever you are.
Everything you need to read the heat.
Validated WBGT
Wet-bulb globe temperature via the full Liljegren (2008) energy-balance method — the occupational and military reference standard, cross-checked against the U.S. National Weather Service.
Seamless global map
A smooth, interpolated heat field for the entire planet. Pan and zoom anywhere; tap any point for its exact reading.
Six heat lenses
Heat Stress, Real Feel, Mugginess, Heat Index and Wet Bulb — plus plain Air Temp as a reference. Switch instantly to read heat the way that matters to you.
7-day & hourly forecast
Daily peaks and an hour-by-hour strip for the metric you care about, with the day's hottest window marked.
Now — and later
Scrub the whole view to any hour ahead: the map and the reading move together, so you can plan around the heat that's coming, not just what's here now.
Watch the day play out
Hit animate and the map runs forward through the next 48 hours, with a scrubber you can grab to stop on the exact hour you care about — labelled with that place's own clock.
Day and night on the map
The night side is shaded and the terminator moves as you scrub, so you can see at a glance where the sun has set — and that a hot reading after dark is heat the ground is still giving back.
A page for how you use it
Outdoor work, athletics, tactical training and paw safety each get their own page: search a place, get that audience's guidance, and share the result — without going through the app.
Activity guidance & state policy
Turns the number into an instruction for general activity, outdoor work, athletics or tactical training — and for U.S. states with a high-school WBGT rule, shows that state's own activity zones alongside it.
A “safe for me” read
Optionally add your situation — how used to the heat you are, how hard you're working, age, health sensitivities — and the guidance escalates for you, never relaxing below the official reading.
Paw & pavement safety
Asphalt in the sun runs 40–60 °F hotter than the air, and a paw pad can burn in about a minute past 125 °F. We estimate the ground temperature — including heat still stored after sunset — so you know before you walk.
Custom heat reports
Pick a place and a date range and get a branded, shareable report — hourly timeline, daily peaks and the windows that matter — as a link, PNG or PDF.
Heat alerts
Save your places and get a push notification when the heat is forecast to cross the level you care about — with quiet hours so it never wakes you at 3 a.m.
Plain-language AI brief
A short, time-aware read on what conditions mean right now and what's coming — written for humans, not meteorologists.
This day in history
How today ranks against the same date across 35 years of reanalysis — the normal, the record, and where today lands.
Installable & offline
Add it to your home screen. It opens instantly, works offline on your last view, and feels like a native app.
Shareable & free
Every place is a link you can send. No account, no paywall, light or dark — just the number you need.
Built for accuracy, open for scrutiny.
Best available data
Leading numerical weather models (ECMWF and national blends, via Open-Meteo) for live conditions, and ERA5 reanalysis for 35 years of history.
Rigorous physics
The full Liljegren (2008) iterative energy balance — solving for the black-globe and natural wet-bulb temperatures, not a rough approximation.
Validated & open
Cross-checked against the U.S. National Weather Service's own WBGT (agreement within about ±1.3°C). Every formula and constant is published.
If heat can hurt you, this is for you.
Athletes & coaches
Call practices and races by the standard governing bodies actually use — including your state's own high-school activity zones.
Outdoor workers
Know when to add water breaks, shade, and rest — before someone goes down.
Parents & caregivers
Judge the playground, the game, the walk — for the people who feel heat hardest.
Dog owners
Check the pavement before you walk: asphalt burns paws long before the air feels dangerous.
Event organizers
Plan around the day's real danger window, not just the forecast high.
Travelers
Understand a climate you've never felt before, anywhere on Earth.
Researchers & media
A transparent, validated, citable heat-stress reference with an open methodology.
Common questions.
What is wet-bulb globe temperature (WBGT)?
WBGT combines temperature, humidity, wind, and direct sun into a single measure of heat stress on the body. It's the standard the military, athletic associations, and occupational-safety bodies use to decide when it's no longer safe to be active outdoors.
How is WBGT different from the heat index?
Heat index estimates how hot it feels in the shade, from temperature and humidity only. WBGT also accounts for wind and direct sunlight, so it reflects real outdoor heat stress — which is why safety organizations rely on it instead.
How accurate is WetBulbTracker?
We use the validated Liljegren (2008) WBGT method and continuously compare our results against the U.S. National Weather Service in public — typically within about ±1.5 °C. The live comparison and our full methodology are open for anyone to inspect.
Is WetBulbTracker free?
Yes. It's free, works anywhere on Earth in any modern browser, and installs to your home screen. A free optional account syncs your saved places and preferences across devices.
What does the “safe for me” personalization do?
You can add optional personal factors — age, heat acclimatization, activity level, and health sensitivities — to get a personalized risk read shown alongside the objective number. It's general guidance, not medical advice.
Why does sun vs. shade matter?
Direct sun can add several degrees of heat stress compared with full shade. WetBulbTracker shows both so you can see how much cooler — and safer — shade really is right where you are.
Heat is the weather hazard we measure least well.
It kills more people in most years than floods, hurricanes, or cold. Yet the number that actually measures it has stayed in safety manuals, costly hardware, and research papers. We’re making it legible to everyone, everywhere — personal, hyper-local, validated in public, and free.