How many hours of daylight a day has

Day length, from sunrise to sunset, depends on two things: where you are and the time of year. At the equator it is almost the same all year; the further you go from it, the more it changes between winter and summer, up to the poles, where months of darkness alternate with months of continuous sun. This calculator estimates the hours of daylight for any latitude and date, how fast the days are getting longer or shorter, and which are the shortest and longest days of the year at that place.

How the calculation works

• Solar declination: the Sun's position relative to the celestial equator, which varies through the year between about +23.4° and −23.4° because of the tilt of the Earth's axis.
• Sunset angle: latitude and declination give how far the Earth turns between noon and sunset.
• −0.833° correction: sunrise and sunset are counted when the Sun's upper edge touches the horizon, and the atmosphere bends light so the Sun is seen a little earlier and later.
• Hours of daylight: twice the sunset angle divided by 15, because the Earth turns 15° every hour.

Latitude is negative south of the equator: in the southern hemisphere the seasons are reversed.

Solstices and equinoxes at different latitudes

Day length in the northern hemisphere at the solstices and the March equinox:

A surprising detail: even at the equinox the day lasts a little over 12 hours, because of refraction and because the Sun is a disc, not a point. For the same reason, the midnight sun can already be seen slightly south of the Arctic Circle.

How days change through the year

Day length on the 21st of each month at 51.5° north, as in London, and at 41.9° north, as in Rome:

Days change fastest around the equinoxes and hardly at all near the solstices: in late March, in London, you gain more than 4 minutes of daylight a day.

The bands of the verdict

• Polar night: the Sun does not rise.
• Under 8 hours: a short day.
• 8 to 12 hours: a day shorter than the night.
• 12 to 16 hours: a day longer than the night.
• Over 16 hours: a long day.
• Midnight sun: the Sun does not set.

Why daylight hours matter

Daylight hours help you plan hikes and trips, estimate solar panel output across the seasons, schedule a vegetable garden and lighting, or simply understand why winter feels so long. Day length also affects the sleep-wake rhythm: in the dark months many people benefit from morning light exposure.

Limits of the calculator

The formula is an approximation: the result can differ by a few minutes from astronomical ephemerides, up to about 10 minutes near the equinoxes. It does not account for mountains or buildings on the horizon, the observer's altitude, or twilight, when there is still light after sunset. Sunrise and sunset times also depend on longitude and time zone, which the calculator does not consider: it estimates the length of the day, not the clock time.

Frequently asked questions

How are daylight hours calculated?

From the latitude and the solar declination, which depends on the day of the year, you get the sunset angle; daylight hours are twice that angle divided by 15. At 41.9° north on 21 December the result is about 9 h 07 min.

Why is the day longer than 12 hours at the equinox?

Because sunrise and sunset are counted from the Sun's upper edge and the atmosphere bends light: you see the Sun a few minutes before it rises and after it sets geometrically.

When do days get longer fastest?

Around the March and September equinoxes. Near the solstices day length barely changes from one day to the next.

How much daylight is there at the winter solstice?

It depends on latitude: about 12 hours at the equator, 9 h 19 min at 40° north, 5 h 52 min at 60° north and none beyond the Arctic Circle.

What is polar night?

The period when, beyond the polar circle, the Sun does not rise for one or more days in a row; in summer the opposite happens, the midnight sun.

How do I enter a place in the southern hemisphere?

With a negative latitude: for example −33.9 for Sydney. The seasons are reversed compared with the northern hemisphere.

Does the calculator give the time of sunrise?

No, it estimates day length. Sunrise and sunset times also depend on longitude, time zone and daylight saving time.

How accurate is the estimate?

Usually within a few minutes, up to about 10 minutes near the equinoxes. For exact times you need astronomical ephemerides.

Do mountains change the result?

Yes: a high horizon makes the Sun rise later and set earlier. The calculation assumes a clear horizon.

Does day length include twilight?

No, it counts only the time between sunrise and sunset. Twilight adds light before and after, for longer at high latitudes.

Where do I find my latitude?

On any online map: it is the first of the two coordinates, positive north of the equator and negative south.

Why do daylight hours matter?

To plan hikes, trips, gardens and lighting, to estimate solar output across the seasons or to understand your sleep-wake rhythm.