# Time Unit Converter

Free time unit converter. Convert between milliseconds, seconds, minutes, hours, days, weeks, months, and years instantly.

## What this calculates

Instantly convert between time units from milliseconds to centuries. This calculator uses the Gregorian calendar average year (365.2425 days) for month and year conversions.

## Inputs

- **Value** — min 0
- **From** — options: Milliseconds (ms), Seconds (s), Minutes (min), Hours (hr), Days, Weeks, Months (avg), Years (avg), Decades, Centuries
- **To** — options: Milliseconds (ms), Seconds (s), Minutes (min), Hours (hr), Days, Weeks, Months (avg), Years (avg), Decades, Centuries

## Outputs

- **Result** — The converted time value.
- **Conversion** — formatted as text — Step-by-step conversion explanation.

## Details

Time conversion is fundamental across science, project management, computing, and everyday life. While small units (seconds, minutes, hours) have exact relationships, larger units (months, years) require averaging due to calendar irregularities.

Exact Relationships

- 1 minute = 60 seconds

- 1 hour = 60 minutes = 3,600 seconds

- 1 day = 24 hours = 86,400 seconds

- 1 week = 7 days = 604,800 seconds

Average Values (Gregorian Calendar)

- 1 year = 365.2425 days (accounts for leap years)

- 1 month = 30.436875 days (365.2425 / 12)

These averages are used by international standards for converting between months/years and smaller units.

## Frequently Asked Questions

**Q: How many seconds are in a day?**

A: There are exactly 86,400 seconds in a day. This is calculated as 24 hours × 60 minutes × 60 seconds = 86,400 seconds. This value is exact and does not depend on leap seconds for civil timekeeping.

**Q: How many days are in a year?**

A: A common year has 365 days, while a leap year has 366 days. The Gregorian calendar averages 365.2425 days per year over its 400-year cycle (97 leap years in 400 years). This converter uses the average value for consistency.

**Q: Why are month conversions approximate?**

A: Calendar months vary from 28 to 31 days, so there is no exact conversion between months and smaller units. This converter uses the average Gregorian month of 30.436875 days (365.2425 days / 12 months).

**Q: How many hours are in a year?**

A: Using the Gregorian average of 365.2425 days per year, there are 8,765.82 hours in a year. A common year (365 days) has 8,760 hours, and a leap year (366 days) has 8,784 hours.

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Source: https://vastcalc.com/calculators/conversion/time-conversion
Category: Conversion
Last updated: 2026-04-21