Choose a Measurement
Select a measurement and convert between different units
Single conversion
To convert from Hour (h) to Day (d), use the following formula:
Let's convert 5 Hour (h) to Day (d).
Using the formula:
Therefore, 5 Hour (h) is equal to Day (d).
Here are some quick reference conversions from Hour (h) to Day (d):
| Hours | Days |
|---|---|
| 0.000001 h | d |
| 0.001 h | d |
| 0.1 h | d |
| 1 h | d |
| 2 h | d |
| 3 h | d |
| 4 h | d |
| 5 h | d |
| 6 h | d |
| 7 h | d |
| 8 h | d |
| 9 h | d |
| 10 h | d |
| 20 h | d |
| 30 h | d |
| 40 h | d |
| 50 h | d |
| 100 h | d |
| 1000 h | d |
| 10000 h | d |
An hour (h) is a universal unit of time equal to 60 minutes, or 3,600 seconds.
The practice of breaking the day into smaller parts goes back to ancient civilizations, especially the Egyptians. They divided daylight and nighttime into 12 hours each, creating the 24-hour day.
During the day, they used shadow clocks—an early form of sundial—to tell the hours, and at night, they tracked groups of stars called decans to mark the hours.
This system, known as a duodecimal (base-12) system, was convenient as the number 12 has many factors, making it easy to subdivide.
The reason we divide an hour into 60 minutes and a minute into 60 seconds comes from the ancient Babylonians. They used a sexagesimal (base-60) numbering system for their mathematical and astronomical calculations.
This system was likely adopted because 60 is a highly composite number, having twelve factors (1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60). This made it exceptionally easy to calculate fractions.
The Greek astronomers Hipparchus and Ptolemy later adopted this system for their astronomical work, solidifying its use in measuring time and angles (like the 360 degrees in a circle).
While an hour is commonly defined as 3,600 seconds, its ultimate precision is tied to the modern definition of a second.
According to the International System of Units (SI), a second is the duration of 9,192,631,770 cycles of the radiation emitted during the transition between two energy levels of the caesium-133 atom.
Therefore, a modern hour equals exactly 3,600 seconds — 3,600 times this atomic standard — making it an exceptionally stable, universally consistent unit of time verified by atomic clocks around the world.
The 24-hour day is the most basic unit we use to organize our lives. But what exactly defines a day, and is it always the same length?
A standard solar day, on which our clocks are based, is the time it takes for the Earth to rotate so that the Sun appears in the same position in the sky. This works out to be 86,400 seconds.
However, the story of a day is a bit more complex.
While we live by the 24-hour solar day, Earth's true rotation period is slightly shorter.
A sidereal day is the time it takes for Earth to rotate 360 degrees on its axis relative to distant stars. This period is actually 23 hours, 56 minutes, and 4 seconds.
So why is the solar day we use about four minutes longer? It's because while the Earth is spinning, it's also orbiting the Sun. After one full rotation (a sidereal day), it has to spin a little bit extra to "catch up" and bring the Sun back to the same point in the sky. That extra rotation time gives us our 24-hour solar day.
Yes, but don't adjust your watch just yet! The length of a day on Earth is slowly increasing.
This is due to a process called tidal braking, where the Moon's gravitational pull creates a slight drag on our planet's rotation, slowing it down.
This effect is minimal, adding only about 1.7 milliseconds to the length of a day every century. Although you may not notice it, it adds up over geological time. For example, when dinosaurs lived, a day on Earth was approximately 23 hours long.
Even though our clocks run on a steady 24-hour cycle, the actual length of a solar day (from one noon to the next) varies slightly throughout the year. The 24-hour day is just an average.
Two main factors cause this variation: