Hours Calculator
PrintTracking the hours spent on a project, calculating elapsed time for work shifts, or auditing a timecard requires subtracting start times from end times. This process is complicated by the transition between AM and PM hours, timezone differences, and varying days in calendar months.
Our free online Hours Calculator lets you find the exact hours and minutes between two points in two modes:
- Hours and Minutes Between Times: Enter a start time (e.g., 8:30 AM) and an end time (e.g., 5:30 PM) to find the elapsed hours. A convenient “Swap” button lets you switch the times instantly.
- Hours Between Two Dates: For longer periods, enter both starting and ending calendar dates alongside their respective hours to get the total cumulative hours.
12-Hour vs. 24-Hour Clock Systems
People read time using one of two standard formats, which can lead to confusion if they are mixed up on a time card:
1. The 12-Hour Clock
The 12-hour clock system divides the 24-hour day into two periods using the numbers 1 through 12:
- AM (Ante Meridiem): Meaning “before midday,” denotes the hours from midnight (12:00 AM) to right before noon.
- PM (Post Meridiem): Meaning “after noon,” denotes the hours from noon (12:00 PM) to right before midnight.
To avoid ambiguity, it is often best to refer to 12:00 AM as 12 midnight and 12:00 PM as 12 noon. Many scheduling errors occur because these two labels are accidentally swapped.
2. The 24-Hour Clock (Military Time)
The 24-hour clock uses a continuous scale from 0 to 23. It runs from 00:00 (midnight) to 23:59, completely eliminating the need for AM or PM indicators.
This format is an international standard and is widely referred to as military time in the United States. It is used in aviation, logistics, emergency services, and medical environments where miscommunicating a 12-hour interval could result in severe accidents.
Hours Contained in Different Time Periods
For long-term planning, contract auditing, or tracking machinery runtimes, the table below provides a breakdown of the total hours within standard calendar divisions:
| Time Period | Number of Hours |
|---|---|
| 1 Day | 24 hours |
| 1 Week | 168 hours |
| 1 Month (28-day month) | 672 hours |
| 1 Month (29-day leap month) | 696 hours |
| 1 Month (30-day month) | 720 hours |
| 1 Month (31-day month) | 744 hours |
| 1 Month (Average calendar month) | 730.5 hours |
| 1 Year (365-day common year) | 8,760 hours |
| 1 Year (366-day leap year) | 8,784 hours |
| 1 Year (Average astronomical year) | 8,766 hours |
| 1 Decade (Average decade) | 87,660 hours |
| 1 Century (100 calendar years) | 876,600 hours |
For more detailed calculations involving calendar intervals, use our Date Calculator, check your exact chronological age with the Age Calculator, or perform mixed operations using the Time Calculator.
Frequently Asked Questions (FAQ)
How many hours are in a standard working year?
For a standard full-time employee working 40 hours per week over 52 weeks, a working year contains exactly 2,080 working hours. This is the baseline number used by human resource departments to calculate annual salaries from hourly wages.
What does AM and PM stand for?
AM stands for the Latin phrase ante meridiem, which translates to “before midday.” PM stands for post meridiem, translating to “after midday.” They mark the divisions of the 12-hour clock system.
How do you calculate decimal hours?
To convert minutes into decimal hours, divide the number of minutes by 60.
Example: If you worked 8 hours and 45 minutes:
45 ÷ 60 = 0.75
Your decimal hours worked is 8.75 hours. This conversion is necessary for multiplying hours by hourly pay rates.
How many hours are in a leap year?
Because a leap year contains an extra calendar day (366 days instead of 365), it contains exactly 8,784 hours. This is 24 hours more than a standard year, which has 8,760 hours.