Inverse Proportion (People × Days)
Treat the work as fixed at people × days. Four people taking twelve days is 48 person-days, so six people take eight. Multiply the crew by 1.5 and the time divides by 1.5.
Your numbers
Days needed
8d
Result
48
Difference
4d
Formula
Days needed = Workers × Days in term ÷ People
In practice coordination costs eat into this, so it is never exactly inverse. Software projects break the assumption hardest.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| WorkersHow many people are on the job. | 4 | 1 and up |
| Days in term (d)The full length of the contract or pass. | 12 | 0 and up |
| PeopleHow many people share it; leave it at one to see the undivided figure. | 6 | 1 and up |
Step by step
Quick reference table
Results when only Workers changes and everything else stays put.
| Workers | Days needed (d) | Result | Difference (d) |
|---|---|---|---|
| 2 | 4 | 24 | 8 |
| 3 | 6 | 36 | 6 |
| 4 | 8 | 48 | 4 |
| 6 | 12 | 72 | 0 |
| 8 | 16 | 96 | -4 |
What each result means
| Result | At default values |
|---|---|
| Days needed (d)Days to finish with that many people. | 8 |
| ResultWhat the formula gives back — the answer this page is for. | 48 |
| Difference (d)The gap between two values — a quantity, not a rate. | 4 |
Common mistakes
In practice coordination costs eat into this, so it is never exactly inverse. Software projects break the assumption hardest.
Glossary
- Workers
- How many people are on the job.
- Days in term
- The full length of the contract or pass.
- People
- How many people share it; leave it at one to see the undivided figure.
- Days needed
- Days to finish with that many people.
- Result
- What the formula gives back — the answer this page is for.
- Difference
- The gap between two values — a quantity, not a rate.
Frequently asked questions
Q. How is Inverse Proportion (People × Days) calculated?
Days needed = Workers × Days in term ÷ People — Treat the work as fixed at people × days. Four people taking twelve days is 48 person-days, so six people take eight. Multiply the crew by 1.5 and the time divides by 1.5.
Q. Can you walk through an example?
With Workers 4, Days in term 12d, People 6, the answer is Days needed 8d.
Q. What do I need to enter?
Enter Workers, Days in term, People. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Workers moves the answer to Workers 2 → Days needed (d) 4 and Workers 8 → Days needed (d) 16. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
In practice coordination costs eat into this, so it is never exactly inverse. Software projects break the assumption hardest.
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