How WhetherWear Decides What You Should Wear
WhetherWear turns a forecast into a clothing decision in a fixed order: it establishes what the air actually feels like, checks for rain and wind, reads how the temperature will move across the hours you will be outside, adjusts for what you will be doing and for how long, and then applies your own stated tendency to run warm or cold.
The order the inputs are applied in
- Forecast and current observation for your location.
- Feels-like temperature. One value, used on every surface in the app. Wind chill governs below roughly 50°F; humidity governs above it.
- Precipitation. Measured amount and probability, and when in the day it falls.
- Wind. Sustained wind, not gusts — a gust does not set what you wear.
- Humidity, cloud cover and UV. How readily sweat evaporates, and how much the sun adds.
- Temperature trajectory. Whether the day is warming or cooling across the hours that concern you.
- Activity. Sedentary, walking, or exercising.
- Time outdoors. How long the clothing has to work for.
- Personal calibration. Whether you have told the app you run warm or cold.
The order matters. Personal calibration is applied last, to a recommendation that is already correct for the conditions, so that a preference adjusts the answer rather than replacing it.
What is published and what is not
Published: the weather provider, the complete list of inputs above, the order they are applied in, the fact that one feels-like value is used everywhere, which correction governs in which temperature range, and how the app behaves when a reading is missing.
Not published: the garment catalogue weightings, the specific threshold constants, and the internal rules that select and adjust individual pieces. Those are the product.
The line is drawn so that anyone can check whether the reasoning is sound without being able to reproduce the output. A method you cannot inspect is not one you should trust; a method published in full is not a product.
The physics it relies on
The temperature corrections are standard published formulas rather than anything invented here:
- NWS wind chill, on air temperature and sustained wind, in the cold range where it is valid.
- NOAA heat index, in the warm range where it is valid.
- Dew point rather than relative humidity as the measure of how readily sweat can evaporate. 90% humidity at 45°F and 90% at 85°F are opposite clothing problems, and only dew point separates them.
What WhetherWear does not know
- Indoor conditions. It has no way to know whether your office is overheated or your commute is on an unheated platform.
- Your wardrobe. Recommendations describe a kind of garment, not a specific item you own.
- Your health. Medication, circulation and illness all change cold and heat tolerance, and none of that is visible to the app.
- Microclimate. A forecast point is not your street. Shade, buildings and water shift real conditions from the reported ones.
Recommendations are comfort guidance. They are not safety instruction, and they are not medical advice. Where weather is severe, follow your national weather service.
What has not been validated
WhetherWear does not claim a measured accuracy rate, and no figure of that kind appears anywhere on this site. Establishing one would require a study comparing recommendations against reported comfort across a real population, and no such study has been run. Until it has, the honest description of the engine is that it applies published thermal-comfort physics through a deterministic rule set — not that it is proven correct.
The engine is deterministic: the same inputs always produce the same outfit. No generative model sits anywhere in the recommendation path.
Related questions
Does WhetherWear produce its own forecasts?
No. It licenses weather data and interprets it as a clothing decision. It is not a forecasting service.
Why do two people get different recommendations in the same place?
Because activity, time outdoors and stated warm/cold tendency all change the answer. Two people can correctly receive different outfits for the same weather.
Does WhetherWear use AI to decide what you wear?
No. The recommendation engine is a deterministic rules-and-thresholds system built on published thermal-comfort physics. The same inputs always produce the same outfit.