What is day?
A day is a unit of time equal to 24 hours, corresponding to one full rotation of the Earth. It is the primary unit for calendars, deadlines, event scheduling, and date-based calculations.
Real-world uses
Days are the fundamental unit for calendars, project deadlines, medication schedules, and billing cycles. Hospital stays, rental periods, and food expiration are counted in days. Astronomers use Julian days for continuous date numbering.
History
The day is one of the oldest natural time units, based on Earth's rotation. Ancient Egyptians were among the first to divide it into 24 hours. The seven-day week originates from Babylonian astronomy, linked to the seven visible celestial bodies.
Common mistakes
Assuming every day is exactly 24 hours. Due to daylight saving time transitions, a day can be 23 or 25 hours. Astronomers also distinguish between solar days and sidereal days (23 hours 56 minutes).
What is second?
The second is the SI base unit of time. It is used globally in science, engineering, computing, and everyday life, and is the foundation upon which all other time units are built.
Real-world uses
The second is the SI base unit of time, fundamental to all scientific measurement, computing clock cycles, athletic timing, and GPS satellite synchronization. Everyday timekeeping, cooking timers, and traffic light cycles all rely on seconds.
History
The concept of dividing the day into 86,400 parts dates to ancient Babylonian and Egyptian timekeeping. Since 1967, the SI second has been defined as 9,192,631,770 periods of the radiation from a caesium-133 atom.
Common mistakes
Assuming a second has always been 1/86,400 of a day. The modern SI second is defined by caesium atom vibrations and is independent of Earth's rotation, which varies slightly due to tidal friction.
When is this conversion used?
Converting day to second is useful in the time domain when comparing values across different measurement standards or applying formulas that require a specific unit.
Worked examples
1 day = 86,400 second
1 second = 1 second
How to convert day to second
To convert day to second, multiply the value by 86,400.
To convert second back to day, multiply by 0.00001157.
Measurement standards
The SI second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium-133 atom, maintained by the BIPM and national metrology institutes worldwide.
Did you know?
Earth's rotation is gradually slowing due to tidal friction with the Moon. To keep atomic time aligned with solar time, "leap seconds" have been inserted 27 times since 1972 — though they are scheduled to be abolished by 2035.
Quick reference: day to second
| day | second |
|---|---|
| 0.1 | 8,640 |
| 0.5 | 43,200 |
| 1 | 86,400 |
| 2 | 172,800 |
| 5 | 432,000 |
| 10 | 864,000 |
| 25 | 2,160,000 |
| 50 | 4,320,000 |
| 100 | 8,640,000 |
| 250 | 21,600,000 |
| 500 | 43,200,000 |
| 1,000 | 86,400,000 |
Common values
| day | second | |
|---|---|---|
| Blink of an eye | 0.00000347 day | 0.3 second |
| Average pop song | 0.00243056 day | 210 second |
| Feature film | 0.08333333 day | 7,200 second |
| One work day (8 hrs) | 0.33333333 day | 28,800 second |
| One calendar year | 365 day | 31,536,000 second |
Available Time units
More day conversions
- Convert day to second
- Convert day to minute
- Convert day to hour
- Convert day to week
- Convert day to year (365 d)
- Convert day to millisecond
- Convert day to microsecond
- Convert day to nanosecond
- Convert day to century (100 yr)
Assumption: year is defined as 365 days and century values are approximate.