Swelter: Heat Index
Heat Stress, WBGT & Safety
Only for iPhone
Free · In‑App Purchases · Designed for iPhone. Not verified for macOS.
iPhone
Know when heat turns dangerous — Swelter reads the heat index from temperature and humidity and flags your risk band. Local conditions worldwide, or type them in.
Swelter turns temperature and humidity into the one number that matters when it's hot: the heat index — the "feels like" temperature your body actually works against — and tells you which risk band you're in before it becomes dangerous.
Built for people who work and train in the heat: construction and field crews, warehouse and kitchen staff, coaches and athletes, event and safety leads.
WHAT YOU GET
• Instant heat index from temperature + relative humidity, using the National Weather Service (Rothfusz) formula
• Clear risk bands — Caution, Extreme Caution, Danger, Extreme Danger — labeled with text, never color alone
• Auto-fill from local conditions anywhere in the world — National Weather Service stations in the United States, Open-Meteo everywhere else — or type readings in by hand when you have no signal
• Fahrenheit and Celsius
• A large, glanceable gauge you can read at arm's length
SWELTER PRO (one-time purchase)
• WBGT estimate (shade) for a fuller read on heat stress
• Home Screen and Lock Screen widgets with your latest reading
• Threshold alerts — get notified when the heat index crosses a level you choose
• Heat log with CSV export to keep a record of the day
NO ACCOUNT. NO TRACKING.
Swelter has no sign-up and no user accounts. Your heat log stays on your device. Location, when you allow it, is used only to fetch the current conditions where you are — it is never stored or shared.
Swelter is an independent app. It is not affiliated with, endorsed by, or connected to the National Weather Service, NOAA, OSHA, or any government agency. Heat-index values and risk bands are based on publicly published National Weather Service guidance. Weather data outside the United States comes from Open-Meteo (CC BY 4.0). Swelter is an informational tool, not a medical, safety, or life-saving device — always follow your organization's heat-safety plan and local regulations.
Ratings & Reviews
- This app hasn’t received enough ratings or reviews to display an overview.
Swelter now works anywhere in the world.
Until now, automatic readings came only from National Weather Service stations, which cover the United States. Outside the US that meant no reading at all, and manual entry every time. Local conditions now come from Open-Meteo everywhere the NWS has no data, so the gauge fills itself wherever you are.
Also fixed: when a reading can't be fetched, Swelter now tells you why — "no data for your location" is not the same problem as a lost connection, and it used to report both the same way.
The developer, Alican Basak, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .
Data Not Linked to You
The following data may be collected but it is not linked to your identity:
- Purchases
- Identifiers
Accessibility
The developer has not yet indicated which accessibility features this app supports. Learn More
Information
- Seller
- Alican Basak
- Size
- 7.8 MB
- Category
- Weather
- Compatibility
Requires iOS 17.0 or later.
- iPhone
Requires iOS 17.0 or later. - Mac
Requires macOS 14.0 or later and a Mac with Apple M1 chip or later. - Apple Vision
Requires visionOS 1.0 or later.
- iPhone
- Languages
- English
- Age Rating
4+
- 4+
- In-App Purchases
Yes
- Swelter Pro $5.99
- Copyright
- © 2026 Alican Başak