# Time conversions

## Select a unit of time

Time is a measurable interval during which something happens, exists or acts in apparently irreversible succession.

The base unit of time in the International System of Units (SI) is the second (s). Other measurable intervals that have long been used as units of time include milliseconds, minutes, hours, days, weeks, months, years, centuries, etc. Although these are non-SI units of time, they are officially accepted to be used along with other SI units.

Time is relative to the system of reference from which the measurement is made.

## Common time conversions

• 1 second = 1,000 milliseconds
• 1 minute = 60 seconds = 60,000 milliseconds
• 1 hour = 60 minutes = 3,600 seconds
• 1 day = 24 hours = 1,440 minutes = 86,400 seconds
• 1 month = 4 weeks
• 1 week = 7 days (5 working days + 2 weekend days) = 168 hours = 10,080 minutes
• 1 year = 12 months = 365 days
• 1 leap year = 12 months = 366 days
• 1 decade = 10 years
• 1 century = 10 decades = 100 years
• 1 millennium = 10 centuries = 100 decades = 1,000 years
• Age of the Universe = about 13.5 billions of years since big-bang, for an observer on Earth
• Age of our Galaxy (Milky Way) = approximately 8.8 billions of years, for an observer on Earth
• Age of the Earth = nearly 5 billions of years, for an observer on Earth

## Units of time measurement

Conversions from and to various units of time.