Umbrella Decision Calculator
Find out whether it's worth taking an umbrella today.
Umbrella recommendation
Yes
Wind of 15 km/h factored in.
Rain exposure risk
Moderate
Estimated time in rain
18 min
Chance of rain applied to your overlap outdoors.
Confidence score
99%
- Runs entirely in your browser
- No data is stored
- Free forever
What is this calculator?
Carrying an umbrella you never open is annoying; getting soaked is worse. This calculator weighs the chance of rain, how long the rain is expected to last, the wind speed and how long you will be outside, then gives a clear yes, probably or no answer along with your rain exposure risk and a confidence score.
How does it work?
Your expected exposure is the chance of rain multiplied by the overlap between the shower and your time outdoors. Strong wind reduces how useful an umbrella is, so it lowers the score. The combined score maps to a recommendation, and confidence rises when the inputs point clearly one way.
Frequently asked questions
When is an umbrella not worth it?+
Below roughly 25 km/h of wind it is fine, but above that gusts flip the canopy and a hooded jacket wins.
What counts as time outdoors?+
Only the minutes actually exposed: walking to the station, waiting for a bus, crossing a car park.
Why does chance of rain not decide it alone?+
A 90% chance of a five-minute shower while you are outside for three minutes barely matters. Overlap is what counts.
What is the confidence score?+
How clear-cut the answer is. Borderline inputs give lower confidence; obvious downpours or dry days give high confidence.
Does it use a live forecast?+
No. You enter the numbers from your own weather app, so it works anywhere without location access.
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