Time is a measure of how long an event lasts, or how long it takes between two occurrences. In the International System of Units (SI), time is measured in seconds with the symbol \( \large s \).

 

 

SI unit of time

 

The fundamental unit of time is the second:

 

$$ \large 1 \text{ s} = \frac{1}{86400} \text{ day} $$

 

A day consists of 24 hours, each hour has 60 minutes, and each minute has 60 seconds. Therefore, there are \( \large 24 \cdot 60 \cdot 60 = 86400 \) seconds in one day.

 

 

Derived units

 

Time can be expressed with prefixes or larger units depending on the context:

 

Factor	Name	Symbol	Unit
\( \large 0.001 \)	Millisecond	ms	\( \large 1 \text{ ms} = 0.001 \text{ s} \)
\( \large 0.01 \)	Centisecond	cs	\( \large 1 \text{ cs} = 0.01 \text{ s} \)
\( \large 0.1 \)	Decisecond	ds	\( \large 1 \text{ ds} = 0.1 \text{ s} \)
\( \large 1 \)	Second	s	\( \large 1 \text{ s} = 1 \text{ s} \)
\( \large 60 \)	Minute	min	\( \large 1 \text{ min} = 60 \text{ s} \)
\( \large 3600 \)	Hour	h	\( \large 1 \text{ h} = 3600 \text{ s} \)
\( \large 86400 \)	Day	d	\( \large 1 \text{ d} = 86400 \text{ s} \)

 

 

Examples

 

• One minute lasts \( \large 60 \text{ s} \).
• One hour consists of \( \large 3600 \text{ s} \).
• One day consists of \( \large 24 \text{ hours} \).