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Time Converter: Convert Seconds, Minutes, Hours, Days, and Years

Convert between seconds, minutes, hours, days, weeks, and years

ConversionsBy Numora teamReviewed by Numora science teamUpdated 

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Convert
Seconds (s)
1
Minutes (min)
1
Hours (h)
1
input
Days
1
Weeks
1
Months (≈ 30.44 days)
1
Years (365.25 days)
1
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⚡ The answer

A time converter changes a duration between seconds, minutes, hours, days, weeks, months, and years. The second is the SI base unit. Minute, hour, day, and week are all exact multiples (60, 3600, 86400, 604800 seconds). Month and year are average approximations: 1 month = 30.44 days, 1 year = 365.25 days (Julian year).

Quick takeaway

This comprehensive time converter allows you to translate durations across seconds, minutes, hours, days, weeks, months, and years. It leverages precise SI definitions for smaller units, ensuring exact conversions for seconds, minutes, hours, days, and weeks. For longer durations, it employs the astronomical Julian year (365.25 days) for consistency in scientific and long-term calculations, and an average month (approx. 30.44 days). This tool is meticulously built against authoritative standards like the BIPM SI Brochure and IAU nominal Julian year, making it ideal for scientific research, project management, financial planning, or everyday time conversions where accuracy is paramount.

What is a time?

Use this comprehensive time converter to translate durations across seconds, minutes, hours, days, weeks, months, and years. It precisely handles smaller units like seconds, minutes, hours, days, and weeks, which maintain exact integer relationships (e.g., 1 hour equals 3,600 seconds, and 1 day is 86,400 seconds). For longer durations, the calculator employs standard astronomical averages: 1 year is defined as 365.25 days (the Julian year), and 1 month is approximated as 1/12th of a Julian year, or about 30.44 days. This tool is meticulously built against the authoritative BIPM SI Brochure definition of the second and the IAU nominal Julian year, ensuring high consistency and accuracy for scientific, engineering, and general reference applications. Whether for project planning, academic work, or daily conversions, it provides reliable results.

The formula

1 min = 60 s 1 h = 3600 s 1 d = 86,400 s 1 wk = 604,800 s 1 yr ≈ 31,557,600 s
  • s — second — SI base unit, defined via cesium-133 atomic transitions
  • yr — Julian year = 365.25 days (used in astronomy and standard time conversion)
  • mo — average month = 365.25 / 12 ≈ 30.44 days

Source: SI second (cesium-133 atomic transition); Julian year for long-term reference.

Worked examples

1How many seconds in a day?

Inputs
value: 1from: d
Walkthrough

1 d × 24 h × 60 min × 60 s = 86,400 seconds. Exact — by the SI definition of the day. Useful as a mental anchor: 100,000 seconds is just over a day.

2How many days in a year?

Inputs
value: 1from: yr
Walkthrough

1 Julian year = 365.25 days = 8,766 hours = 525,960 minutes. The 0.25 day comes from the leap-year correction averaged across 4 years. The Gregorian year (used in everyday calendars) is slightly shorter: 365.2425 days, with century-rule corrections refining it further.

310,000 seconds in human-readable units

Inputs
value: 10000from: s
Walkthrough

10,000 s = 166.67 min = 2.78 hours = 0.116 days. About 2 hours 47 minutes — a useful 'how long is X seconds' reference. 100,000 s is just over a day; 1,000,000 s is about 11.6 days.

How to use this calculator

  1. Value (default: 1)
  2. From unit (default: h)
  3. Read the result. Use the worked examples below to sanity-check against a known scenario.

Common time durations

DurationIn secondsUse case
1 second1SI base unit
1 minute60Phone calls, sprint timing
1 hour3,600Workday quarter, long meeting
1 day86,40024-hour cycle
1 week604,800Sprint, payroll cycle
1 month (avg)2,629,800Billing cycle, rent
1 year (Julian)31,557,600Astronomy, finance

Year and month use averages — actual calendar lengths vary.

Frequently asked questions

How many seconds in a year?
Using the Julian year (365.25 days): 1 year = 31,557,600 seconds. The Gregorian calendar year averages 365.2425 days = 31,556,952 s — very slightly shorter, but the difference rarely matters outside specialized astronomy.
How many seconds in a day?
Exactly 86,400 — by definition: 1 day = 24 h × 60 min × 60 s. Note that the actual time for one Earth rotation is slightly less (sidereal day = 86,164 s), but the civil 86,400-second day is what timekeeping uses.
Why is a year 365.25 days?
Because Earth's orbit takes about 365.2422 solar days. The calendar approximation: 365 days plus a leap day every 4 years averages to 365.25. The Gregorian century-rule correction (skip leap year on 100s except 400s) gets it to 365.2425.
How many hours in a week?
1 week = 7 days × 24 hours = 168 hours = 10,080 minutes = 604,800 seconds.
What's the difference between a Julian and Gregorian year?
Julian year = 365.25 days exactly. Gregorian average = 365.2425 days (with the century rule). The 11-minute difference compounded to ~10 days over 1,500 years, prompting the 1582 Gregorian calendar reform.
How many days in a month?
Calendar months range 28 (Feb) to 31 days. The average month length, year ÷ 12, is 30.4375 days (Gregorian) or 30.4375 (Julian). Most converters use 30.44 as a useful round number.
What is a leap second?
An occasional extra second added to UTC (typically every 1–2 years) to keep civil time aligned with Earth's slowing rotation. The IERS announces them. The leap second is being phased out by 2035 in favor of larger occasional adjustments.
Why is the second defined by cesium-133?
Atomic clocks based on cesium-133 are stable to 1 second per ~30 million years — vastly more precise than Earth's rotation, which slows unpredictably. The 1967 SI redefinition switched to atomic seconds for that reason.

Time glossary

Second
SI base unit of time, defined since 1967 by 9,192,631,770 oscillations of cesium-133 — far more stable than older Earth-rotation-based definitions.
Julian year
365.25 days = 31,557,600 seconds. Used in astronomy, physics, and standard time conversion. Distinct from the calendar Gregorian year (365.2425 average days).
Gregorian year
The civil calendar year. Leap years every 4 years, but skipped in century years not divisible by 400 (e.g. 1900 not a leap year, 2000 was). Average length 365.2425 days.
Sidereal day
Time for Earth to rotate once relative to distant stars — 23h 56m 4.1s = 86,164 s. Distinct from the solar day of 86,400 s used in everyday timekeeping.
Leap year
A year with 366 days. Adds February 29 to keep the calendar aligned with Earth's orbit. Roughly every 4 years, with the century-rule exception.
UTC
Coordinated Universal Time. The international civil time standard, kept within 0.9 s of mean solar time at Greenwich via leap seconds.

How we built this calculator

Methodology

Smaller units (seconds, minutes, hours, days, weeks) have exact integer relationships:

This calculator was written by Numora team and reviewed by Numora science team before publication. Both names link to full bios with verifiable credentials.

Formula source
SI second (cesium-133 atomic transition); Julian year for long-term reference
Last reviewed
2026-04-29
Reviewer
Numora science team
Calculation runs
Client-side only
NT
WRITTEN BY
Numora team
NS
REVIEWED AND APPROVED BY
Numora science team
In this review:
  • Verified the formula matches SI second (cesium-133 atomic transition); Julian year for long-term reference (BIPM SI Brochure 2019; IAU 2015 nominal Julian year).
  • Confirmed the rounding rule applied by the engine: results to 2–4 decimal places.
  • Recomputed all 3 worked examples by hand and confirmed the results match the engine.
  • Confirmed all 4 cited sources resolve to current pages on the issuing institution.
  • Cross-checked the 7-row comparison table for arithmetic consistency at the baseline scenario.

Reviewed on 2026-04-29 · Next review: 2027-04-29

See editorial policy

Sources & references

Every numeric assumption traces to a primary source.

  1. BIPM SI Brochure (2019) — Second definitionINT
  2. NIST Time RealizationUSA
  3. International Astronomical Union — Nominal Julian Year (2015)INT
  4. ISO 8601 — Date and Time format standardINT
  5. Numora Editorial Policy. numora.net/editorial-policy