Time Converter
Milliseconds, seconds, hours, days and weeks up to years, using average months and years
Milliseconds, seconds, hours, days and weeks up to years, using average months and years. No data leaves your browser – every conversion happens locally.
Fixed units versus the calendar
Seconds, minutes, hours, days and weeks never change length, so those conversions are exact. Months and years don't have a fixed length, so this tool uses averages: a month is 30 days and a year is 365 days.
That means "1 year in months" shows 12.17, not 12. It's the right answer for rough planning (how many weeks are in 18 months?) and the wrong one for anything tied to real dates, like notice periods or loan tenures. For those, use the Date Difference calculator, which counts actual calendar days including leap years.
Time unit reference
| 1 minute | 60 seconds |
| 1 hour | 3,600 seconds |
| 1 day | 86,400 seconds |
| 1 week | 604,800 seconds |
| 1 year (avg) → days | 365 days |
| 1 year (avg) → seconds | 31,536,000 seconds |
Worked examples
One million seconds
It's 11.57 days. A billion seconds, by contrast, is about 31.7 years.
A 90-day trial
90 days is 12.86 weeks, just short of three calendar months.
Video timestamps
Editors often log in milliseconds. 45,000 ms is 45 s, and 3,600,000 ms is exactly one hour.
Common durations in hours, minutes and seconds
This table uses the same fixed lengths the converter does: 30-day months and 365-day years. The first four rows are exact; the last two are averages.
| Duration | Hours | Minutes | Seconds |
|---|---|---|---|
| 1 hour | 1 | 60 | 3,600 |
| 8-hour shift | 8 | 480 | 28,800 |
| 1 day | 24 | 1,440 | 86,400 |
| 1 week | 168 | 10,080 | 604,800 |
| 1 month (30 days) | 720 | 43,200 | 2,592,000 |
| 1 year (365 days) | 8,760 | 525,600 | 31,536,000 |
Decimal hours on timesheets
Payroll and billing systems often record time as decimal hours, and that's where most time-conversion errors come from. 1.5 hours is 1 hour 30 minutes, not 1 hour 50. 7.25 hours is 7 hours 15 minutes. To go the other way, divide the minutes by 60: 7 hours 40 minutes is 7.67 hours.
Also keep in mind that a real year averages 365.2425 days. That's 20,952 seconds, about 5.8 hours, more than the 365-day year this tool uses. Over a single year it barely matters. Over a 30-year span it adds up to about a week.
Developers hit a third version of this. JavaScript's Date.now() counts milliseconds, while most Unix timestamps count seconds. Read 1,700,000,000 as milliseconds by mistake and you get a date about 19.7 days after 1 January 1970 instead of November 2023.