Enter the rain probability shown in your weather forecast (for example "60% chance of rain") and pick the type of precipitation expected, to see what the percentage actually means and how long the rain might last if it happens.
This percentage does NOT mean:
that it will rain during that percentage of the time period (a 60% forecast is not "it will rain 60% of the time").
that it will rain over that percentage of the geographic area (a 60% forecast is not "60% of the region will get wet").
The official formula used by forecasters is: Probability of Precipitation = Forecaster Confidence x Areal Coverage. In other words, it combines how sure the forecaster is that rain will occur somewhere in the area with how much of that area is expected to be affected.
What a percent chance of rain really means
When a forecast shows a percentage next to a rain icon, most people assume it means "it will rain during that percentage of the day" or "that percentage of the area will get wet". Neither is correct. The figure is the Probability of Precipitation, a single number defined by forecasters as Confidence multiplied by Areal Coverage: how sure they are that measurable rain will fall somewhere in the forecast area, combined with how much of that area is expected to see it. A 60% forecast could mean the forecaster is completely certain that rain will fall, but only over 60% of the region, or it could mean the forecaster is only 60% sure at all, with rain covering the whole area if it happens.
Interpretation by percentage range
| Forecast percentage | Plain-language meaning | Umbrella advice |
|---|---|---|
| 0 to 10% | Very unlikely, essentially a dry forecast | Not needed |
| 10 to 30% | Low chance, isolated showers possible | Not needed |
| 30 to 50% | A real possibility but not more likely than not | Take one as a precaution |
| 50 to 70% | Likely | Recommended |
| 70 to 90% | Very likely | Take a raincoat |
| 90 to 100% | Near certain | Take a raincoat |
The official formula: Confidence x Areal Coverage
The formula behind this figure comes from the US National Weather Service, but the same underlying idea is used across weather services worldwide: Probability of Precipitation equals the forecaster's confidence that rain will develop, multiplied by the fraction of the area expected to be covered by that rain. It is a single combined number, so the same 40% can describe two very different situations: a fairly confident forecast of scattered showers over less than half the area, or a less confident forecast of widespread rain across the whole area. The percentage never tells you which of the two it is, and it says nothing about how long the rain will last if it arrives, which is why this guide also asks for the expected precipitation type.
How the UK Met Office presents this figure
The Met Office shows the "chance of rain" as an hour-by-hour percentage for the day ahead, alongside a rain radar and detailed short-range guidance, which is more granular than a single daily figure. In the UK, unsettled weather makes moderate percentages (30 to 60%) common for much of the year, and it is worth remembering that even a modest figure such as 30% is not a promise of a dry day, since a short shower can still interrupt an otherwise dry afternoon. For a related look at how humid or muggy a day will feel once rain has passed, see the dew point calculator.