Almost every major weather app on the market asks you to make a choice upfront: Celsius or Fahrenheit. You pick one, it becomes your unit, and you're done.
That works perfectly if you live in one country your entire life. Things gets trickier the moment you step outside of it.
The myth of "getting used to it"
When you move abroad or if you travel a lot, you tell yourself you'll eventually pick up the local temperature scale. You assume it's just a matter of time before the numbers start to make sense.
Years later, an American in London still doesn't stop thinking in Fahrenheit. A British person in New York still has no instinct for what 85°F feels like. The disorientation runs incredibly deep, and it doesn't resolve with time as quickly as people expect.
That's because temperature intuition isn't mathematical – it's emotional. Research in embodied cognition shows that physical temperature is deeply tied to how we process and remember experience – a link explored in Williams & Bargh (2008, Science). When you move countries, that felt vocabulary doesn't transfer with you. And the standard solution of converting the other unit in your head – forces you to do mental maths every time you check the weather. Seven days a week. For years.
Why the unit toggle is a broken design pattern
To solve this, most weather apps (like Apple Weather or AccuWeather) offer a unit toggle. You tap a button or dig into the settings, and you switch between °C and °F. It seems like a logical feature. But it completely misunderstands the problem.
When you toggle, you look at one unit. Then you toggle back, and you look at the other. You are sequentially reading two numbers and trying to hold both references in your head. That is still a translation step. It treats temperature like a global setting – like Dark Mode vs. Light Mode – rather than what it actually is: a bilingual conversation.
This friction peaks in mixed-nationality households. If you and your partner use different systems, one of you is always staring at a number that means absolutely nothing to them. Toggling doesn't solve the problem; it just passes the frustration back and forth.
Designing a bilingual weather app
People living between two temperature scales don't need a converter. They need a translator.
We realized the only way to remove the friction was to design a weather app that didn't have a settings toggle at all. It needed to show both Celsius and Fahrenheit at the same time. Neither number could be primary. Neither could be a sub-text conversion of the other. They just had to sit side-by-side.
That is what Felsius does. You open the app, you look at the screen, and whichever number your brain recognizes first – that's the one you read. It's the UI equivalent of removing a step.
It's free, has no ads, and is available on iOS and Android. Built for expats, travelers, and anyone who's good with not doing maths every time they check the weather.