THE SHORT ANSWER
Three people, half an hour each: 1.5 person-hours
If all three work from 9:00 to 9:30 a.m., the job takes 30 minutes from start to finish. Add each person's 30 minutes and you get 90 minutes of work, or 1.5 person-hours. Both numbers are correct; they answer different questions.
Total effort and time on the clock are different
Imagine three people cleaning up after an event. Someone waiting for the room needs to know when cleanup will end. Someone keeping a record of the team's work needs the total time everyone contributed.
Person-hours means the sum of each person's work time, measured in hours. One person working for an hour contributes one person-hour. Two people working for half an hour each also contribute one person-hour.
When everyone works for the same length of time, multiply the number of people by that duration. When people arrive late or leave early, add their individual durations instead. The times below are made-up examples.
Add each person's time when schedules differ
Scroll sideways to see the full table.
| Person | Session (a.m.) | Time worked | Hours:minutes input |
|---|---|---|---|
| A | 9:00–10:00 | 60 minutes | 1:00 |
| B | 9:30–10:00 | 30 minutes | 0:30 |
| C | 10:00–10:15 | 15 minutes | 0:15 |
The work adds up to 60 + 30 + 15 = 105 minutes, or 1.75 person-hours. The elapsed time, from 9:00 to 10:15 a.m., is 75 minutes. A and B's overlapping half hour counts once for each person when you add their work.
The durations alone—60, 30, and 15 minutes—cannot tell you the elapsed time. You also need to know when people started and stopped, including whether they worked at the same time.
Watch for breaks, repeats, and totals counted twice
- Decide what the record includes. One person working from 9:00–9:30 and 10:00–10:30 a.m. does one hour of work across a 90-minute span. If the record excludes the half-hour break, add the two work sessions separately.
- Keep equal durations from different people. Three people working for 30 minutes each need three
0:30entries. Removing duplicate lines would erase real work. - Don't add a total to its own parts. A row labeled “whole team: 90 minutes” already includes the three 30-minute entries.
If two overlapping entries belong to the same person, count that person's time only once. This is a way to organize work durations, not a rule for deciding which breaks or waiting periods count as paid time.
Enter durations, not start and finish times
For the staggered sessions above, choose the hours:minutes format, enter these three lines, and select “Add durations.”
Durations for the staggered sessions
1:00 0:30 0:15
The result is 1:45:00, 105 minutes, or 1.75 decimal hours. Because each entry represents someone's work, that total means 1.75 person-hours. The calculator does not infer the number of people or the elapsed time.
To try the opening example of three people working for 30 minutes, enter the same duration three times. The result is 1:30:00, or 1.5 hours.
Three people working for half an hour each
0:30 0:30 0:30
The tool does not subtract start times from finish times or remove breaks and overlaps. In hours:minutes mode, 9:00 means nine hours—not 9:00 a.m.
Person-hours don't promise a finish time
If a job used 1.5 person-hours last time, three people won't necessarily finish it in 30 minutes next time. Some steps depend on earlier ones, people may have to wait, and not every task can be shared. Use the total as a record of time spent, then consider how the work is organized when estimating the next job.
For the difference between 1:45 and 1.75 hours, see how to add hours and minutes and convert to decimal hours.