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The day is a derived unit of time.

\(\ds \) \(\) \(\ds 1\) day
\(\ds \) \(=\) \(\ds 24\) hours
\(\ds \) \(=\) \(\ds 60 \times 24\) \(\ds = 1440\) minutes
\(\ds \) \(=\) \(\ds 60 \times 60 \times 24\) \(\ds = 86\, 400\) seconds


The symbol for the day is $\mathrm {day}$ or $\mathrm d$.

Also known as

The day as defined here is also known as a solar day so as to distinguish it from the sidereal day.

Historical Note

Until $1967$, when the second was redefined to be the SI base unit of time, the day was the fundamental unit of time.

It was defined as being the length of time it takes the Earth to rotate once on its axis relative to the sun.