Daylight Hours Calculator
Tells you how long the Sun is up on a given date at a given latitude, and how that swings through the year.
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
The formula
daylight = 2 × H ÷ 15° per hour cos H = (sin(−0.833°) − sin φ × sin δ) ÷ (cos φ × cos δ)
This is the NOAA solar calculation. Longitude only matters very slightly, through the moment the Sun’s declination is taken.
What to watch out for
The further from the equator, the bigger the swing between summer and winter. It changes fastest near the equinoxes and hardly at all near the solstices.
Frequently Asked Questions
How long is the longest day in London?
About 16 h 38 min. The shortest, in December, is about 7 h 50 min.
How long is the day at the equator?
About 12 h 7 min all year round, as the Sun’s path barely changes in length there.
What are polar day and polar night?
Above the polar circles, around midsummer the Sun does not set, so the day is 24 hours. Around midwinter it does not rise, so the day is zero.