This app calculates the Wet Bulb Globe Temperature (WBGT) to assess outdoor heat risk for activities. It provides clear safety flags and hourly forecasts to help you plan outdoor events safely. Get personalized alerts and find the best times for your activities.
1.4.8
September 10, 2026
Fixed a cosmetic bug with temperature readings displayed in Celsius. Small refinements to the heat index / feels like / wind chill labels in the app.
Every Swelter Pro feature, billed monthly.
$39.99
Swelter Pro Lifetime
Every Swelter Pro feature, forever. One time purchase.
Ask Siri for the current heat risk outdoors.
Aug 31, 2026 — Sep 30, 2026
Thanks for using Swelter, enjoy the time outdoors! 😎🐈
Swelter calculates WBGT by considering air temperature, humidity, wind, and sun strength. This provides a more accurate measure of heat stress than air temperature and heat index alone.
No, Swelter does not contain advertisements. The app is supported entirely by Swelter Pro subscriptions.
Swelter Pro unlocks full week charts, hourly UV and precipitation data, additional alert types, year-over-year trends, saved locations, and the complete widget set. Free users retain core safety features.
Swelter is validated against a large network of WBGT stations, with 99.94% of readings within one flag level compared to 10,760 station-hours of data.
Swelter has an age rating of 12+, making it suitable for users aged 12 and older.
Swelter was last updated on August 6, 2026, with the latest version being 1.1. This indicates regular maintenance and potential feature additions.
Swelter is available for iPhone and iPad devices, allowing users on Apple's mobile platforms to access its heat safety features.
Swelter Pro offers monthly subscriptions at $2.99 per month and yearly subscriptions at $14.99 per year. The yearly plan includes a 7-day free trial.