Hours to days and days to hours converter
Hours to days: divide by 24, so 100 h = 4.167 d, which is 4 days and 4 hours. Type hours and the days update as you type, with the days-plus-hours split and workdays underneath; days to hours works in the same box.
Example: Time 100 · Direction: Hours to days (h → d) → Answer: 100 h = 4.167 d. Source: BIPM – The International System of Units (SI Brochure, 9th edition): day = 86,400 s, hour = 3,600 s (non-SI units accepted for use). Updated: .
How it is calculated
The rule
days = hours ÷ 24 and hours = days × 24. So 72 h = 3 d, 36 h = 1.5 d and, back again, 7 d = 168 h. When the result has a fraction, read it as a share of a day, not as hours: 4.167 days is 4 days and 0.167 × 24 = 4 hours. The line under the answer does that split, which is 4 days 4 hours for 100 h.
Calendar days versus workdays
If the 100 hours are a project estimate, the number you need is probably not calendar days. At 8 working hours a day, 100 h is 12.5 workdays, so about 2.5 working weeks, not 4 days. A 40-hour week is 5 workdays; 160 hours is a typical month of 20 workdays (6.667 calendar days of continuous work, which nobody does). State which kind of day you mean whenever a deadline depends on it.
Shipping windows and uptime
“Delivery in 72 hours” is 3 calendar days, but a promise of “3 business days” skips weekends, so a Friday order may take 5 calendar days. For service levels, a yearly uptime of 99.9 % allows 0.1 % of the 8,760 hours in a year to be down: 8.76 hours, or 0.365 days. At 99.99 % that shrinks to 52.56 minutes.
Months and years in hours
A 30-day month has 720 hours and a 31-day month 744. A common year of 365 days is 8,760 hours; a leap year of 366 days is 8,784 hours. The Gregorian average year of 365.2425 days is 8,765.82 hours, which is why the calendar needs leap years.
Daylight saving
Clocks make the day 23 hours long in spring and 25 hours long in autumn in places with daylight saving. This converter always divides by 24; for exact elapsed time across a changeover use the time calculator. For minutes see minutes to hours.
Frequently asked questions
How many days is 48 hours?
48 h = 2 d. Exactly two days, with no fraction.
How do I convert hours to days?
Divide by 24. For 100 hours: 100 ÷ 24 = 4.1667, which is 4 days and 4 hours, so 100 h = 4.167 d.
How many hours are in a week?
7 d = 168 h, so 168 hours.
How many hours is 3 days?
3 d = 72 h. Multiply days by 24.
How many hours are in a year?
365 d = 8,760 h in a common year and 366 d = 8,784 h in a leap year.
Sources and legal basis
As of: · Editorial policy
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