When SunFinder compares a destination with your home, the first thing it looks at is sunshine hours. It is a less familiar number than temperature or rain probability, but for anyone who simply wants a bright day, it is the most useful one. Here is what it means and how to read it.
The definition
Sunshine duration, or sunshine hours, is the time during which direct sunlight reaches the ground with an intensity of at least 120 watts per square metre. This threshold was set by the World Meteorological Organization (WMO) so that measurements from different countries can be compared. In practice, it corresponds roughly to the moment when objects start to cast clear, sharp shadows.
Diffuse daylight on an overcast day does not count, however bright it seems. Neither does sunlight very close to sunrise and sunset, when the sun is low and weak.
How it is measured
For more than a century, sunshine was measured with a Campbell–Stokes recorder: a glass sphere that focuses sunlight onto a card, burning a trace whenever the sun is strong enough. Counting the length of the burn gave the day's sunshine hours.
Today, most weather stations use electronic sensors that measure direct radiation continuously. Forecasts of sunshine hours come from weather models, which calculate cloud cover and radiation hour by hour. Some services estimate sunshine from satellite images for places without a station.
Sunshine hours versus daylight
The maximum possible sunshine on any day is the length of daylight, minus a little at each end when the sun is too low. This depends strongly on latitude and season:
- Around midsummer, Stockholm or Helsinki have more than 18 hours of daylight, Berlin and Amsterdam about 16.5, Paris about 16 and Rome about 15.
- Around midwinter, Stockholm has about 6 hours, Berlin and Amsterdam about 7.5, Paris about 8 and Rome about 9.
This is why weather services often also publish the percentage of possible sunshine. Six hours of sun is a perfect December day in Berlin but a cloudy one in June.
When comparing places for a trip, the absolute number of hours is what you experience, so SunFinder shows hours a day. In winter, going south adds both clearer skies and longer days.
Typical values across Europe
Annual totals, based on long-term averages and rounded:
- Northern and western Europe: London about 1,500–1,600 hours, Paris 1,700–1,800, Berlin, Copenhagen and Stockholm 1,700–1,900.
- Central and southern Europe: Munich and Vienna about 1,800–2,000, Rome and Barcelona about 2,500–2,600.
- The sunniest regions: south-eastern Spain, the Algarve, Malta, Greece and Cyprus at about 2,700–3,400.
The seasonal pattern also differs. Northern Europe gets most of its sunshine between April and August; around the Baltic, May to July are typically the sunniest months, and coasts and islands often get more sun than inland areas in early summer. In the Mediterranean, July is usually sunniest, but winter still brings 4–6 hours on average.
What a sunshine forecast tells you
A daily forecast of sunshine hours summarises how bright the day will be better than an icon does:
- 0–2 hours: grey or mostly cloudy.
- 3–5 hours: mixed, with sunny spells.
- 6–9 hours: a bright day for most of the year.
- 10+ hours: a properly sunny day, only possible from spring to early autumn in most of Europe, or with long summer days further north.
Two cautions:
- Low cloud and fog are hard to forecast. Sea fog on coasts in spring and early summer, and fog in valleys and basins in autumn and winter, can cut sunshine far below the forecast.
- Afternoon showers. On warm, unstable days, a sunny morning can turn into a cloudy, showery afternoon. The total may still look good, so check the hourly view if timing matters.
Using sunshine hours for trips
The most practical way to use sunshine hours is to compare. An absolute number means little on its own; what matters is the difference between home and the places you could reach:
- A difference of 1–2 hours a day is often within forecast uncertainty and usually not worth a long journey.
- 3–4 more hours a day is clearly noticeable.
- 5 or more hours a day, for example 8 hours of sun instead of 2, is the kind of difference that makes a trip transformative.
This is how SunFinder ranks destinations. It calculates the sunshine hours for your dates at home and at every place within reach, and weighs the gain against the travel time. Combine it with temperature, rain amount and wind, as explained in how to read a weather forecast, and you have a solid basis for deciding whether the sun somewhere else is worth the trip.