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Convert time units
Any unit to any unit, through seconds.
TIME & DATE TOOL
Time Unit Converter
Convert any time unit to any other — seconds, minutes, hours, days, weeks, months, and years — with the month and leap-year traps spelled out, not hidden.
Every conversion runs through seconds
Time units look irregular — 60 seconds, 24 hours, 7 days, 12 months — but they all collapse into one trick: convert to seconds first, then divide into the target unit. A week is 7 × 24 × 3,600 = 604,800 seconds; divide that by 86,400 and you get 7 days back. The calculator above does exactly this two-step on your numbers, so any pair of units converts cleanly.
A worked example
How many seconds in a year? Start at the bottom: one day holds 24 × 60 × 60 = 86,400 seconds. A common year has 365 days, so 365 × 86,400 = 31,536,000 seconds. A leap year adds one day: 366 × 86,400 = 31,622,400 seconds. And the long-run average year (365.25 days, leap years folded in) holds 31,557,600 seconds — the figure to use for anything measured "per year" over many years.
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Converted amount | value × s(from) ÷ s(to) | s(unit) = seconds in one unit. Two multiplications, zero tables to memorize. |
| In seconds | value × s(from) | The universal middle step every conversion shares. |
| In days | seconds ÷ 86,400 | 86,400 = 24 × 60 × 60, the anchor number of time math. |
| In average years | seconds ÷ 31,557,600 | 31,557,600 = 365.25 × 86,400; the long-run year. |
The month trap
Months refuse to convert exactly: 28 to 31 days means "3 months" is not one number of seconds. This page uses the average month of 30.436875 days (365.25 ÷ 12 = 2,629,746 seconds), the standard convention for subscriptions, rent math, and "per month" rates. For an exact calendar stretch — January 5 to April 5 — count the days directly instead of trusting any converter.
Who uses this
- Programmers: timeouts, cron intervals, and token expiries live in seconds or milliseconds — this is the "how long is 90 days in seconds" answer (7,776,000).
- Payroll and billing: converting salaries between per-hour, per-week, and per-month rates starts with clean unit math.
- Students: dimensional-analysis homework is exactly this two-step, dressed up.
- The curious: your age in seconds, a decade in hours — the tile row answers the classic trivia in one click.
Accuracy & limitations
Conversions between fixed units (seconds through weeks) are exact. Months and years use the stated averages — real calendar months and specific years vary, and leap seconds exist in UTC (about 27 added since 1972; this page, like every civil converter, ignores them). For sub-second precision work, use milliseconds or microseconds directly instead of fractional seconds.
Working with clock times instead of durations? The military time converter and Zulu time converter handle time-of-day, and the decimal time converter handles payroll hours.
Cite this calculatorBright Side Kit. “Time Unit Converter.” brightoolbox.com, 2026.
Bright Side Kit. "Time Unit Converter." https://brightoolbox.com/time-unit-converter/ Accessed October 22, 2026.Frequently asked questions
How many seconds are in a year?
A common (365-day) year holds 31,536,000 seconds (365 × 86,400). A leap year holds 31,622,400. The long-run average year (365.25 days) holds 31,557,600 — use that one for multi-year averages. Try it on the time unit converter above.
How many seconds are in a day?
86,400 — 24 hours × 60 minutes × 60 seconds. This is the anchor number behind almost all time math; memorize it and every other conversion becomes one division away.
How many seconds are in a month?
It depends on the month: 2,419,200 (February) up to 2,678,400 (31-day months). Converters standardize on the average month of 2,629,746 seconds (30.436875 days). For billing, check whether your contract means calendar months or the 30-day average.
Why 60 seconds in a minute?
The Babylonians counted in base 60, and the convention survived through Greek astronomy into modern clocks. Sixty divides evenly by 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30 — more clean divisors than any smaller number, which is why the system never died.
How do I convert hours to seconds?
Multiply by 3,600: 2.5 hours × 3,600 = 9,000 seconds. The pattern is always the same — multiply down the ladder (days→hours→minutes→seconds), divide going up.
What is the difference between a common year and a leap year in seconds?
Exactly one day: 86,400 seconds. Common = 31,536,000; leap = 31,622,400. Leap years add February 29 roughly every 4 years to keep the calendar aligned with Earth's orbit (with century exceptions).
How many weeks are in a year?
About 52.18 — 365 ÷ 7. The leftover day or two is why your birthday shifts weekdays each year, and why ISO calendar nerds occasionally declare a 53-week year.