Weather apps are, as a category, extraordinarily good at what they do. They display accurate forecasts, radar images, and hourly breakdowns. They load fast and work offline. They have beautiful designs and smart widgets.
There is one thing most of them get wrong, and it's not a technical problem. It's a design assumption about who is using the app.
The single-country assumption
Every major weather app was built around a core assumption: the user lives in one country, uses that country's temperature scale, and needs the weather translated for one consistent set of intuitions. This assumption works for most users. It just doesn't work for a significant and growing minority.
The number of people living internationally, in mixed-nationality households, or travelling regularly between Celsius and Fahrenheit countries has grown substantially. The UN estimates 281 million international migrants worldwide – a population that spans countries using different temperature standards daily. For those people, a weather app designed around one unit isn't fully solving the problem. It's giving them one piece of the answer and leaving them to do the rest themselves.
Why the toggle is a patch, not a fix
The unit toggle – the setting that switches between °C and °F – is the standard solution. It's a reasonable feature for occasional use. It doesn't solve the problem for people who need both units at once.
When you toggle, you see one number. To compare, you toggle back and see the other. You're holding two sequential readings in short-term memory and trying to synthesise them. That cognitive step – the act of holding and comparing – is exactly the friction that makes temperature switching so tiring.
Toggle also treats temperature as a global setting, like Dark Mode or notification sounds. But for an international household, temperature isn't a device preference – it's a communication problem. Two people in the same room can have different intuitions about the same number. One toggle can't address both of them simultaneously.
Who gets left out
The people who experience this friction every day are not a small group. They include:
- Expats and immigrants who've moved to a country with a different temperature scale
- People in international relationships or households
- Business travellers and remote workers who split their time across countries
- Anyone communicating regularly about weather with family or colleagues abroad
None of these people are confused about temperature. They understand both systems. The problem is that the apps they use were not designed for their situation – and the workaround they use (mental math or toggling) adds friction to something that should be frictionless.
What a different design looks like
The alternative is not to add more features. It's to remove the underlying assumption. If a weather app shows both °C and °F on the same screen without requiring a toggle or settings change, the problem disappears entirely.
Both numbers are present. Each person reads the one their brain recognises. Nobody toggles. Nobody converts. The app becomes a genuinely bilingual tool rather than a monolingual one with a workaround bolted on.
That is the design philosophy behind Felsius. Not a better toggle. Not a smarter converter. Just both numbers, always visible, equally weighted – so whoever picks up the phone already sees what they need.