Practical tools for measured work
Half-life calculator
Solve remaining amount, elapsed time or half-life for exponential decay.
Calculate the layout, check the diagram, then print the result for the shop or jobsite.
How it works
Remaining amount = initial amount × 2^(−elapsed time/half-life). Inverse calculations use the logarithm of the initial-to-remaining ratio. An initial amount of 100 becomes 12.5 after three half-lives.
Current-input example
The result above uses these exact values. This snapshot is included when the page is printed so the output can be checked against the original measurements.
- Decay calculation
- Remaining amount
- Initial amount
- 100
- Elapsed time
- 30
- Half-life
- 10
Primary result: Remaining amount: 12.5.
Before using the result
- Check the selected mode, units and input values before using the result.
- Read the assumptions and rounding rules; compare the worked example with your intended calculation.
- A numerical result does not supply missing context or change the stated limitations.
Limitations
Use one consistent time unit and one consistent amount unit. Assumes a constant exponential decay rate with no replenishment or daughter contribution. It is not a medication dosing or radiation exposure calculator. Inverse calculations require remaining amount strictly between zero and the initial amount.
Frequently asked questions
What should I verify before using this result?
Check the input values, units, dates and assumptions. Compare the method and its stated limits with the source relevant to your task.
Why might the finished result differ?
Results depend on the entered data and the model’s assumptions. Rounding, changing conditions or omitted factors can affect the comparison. Read the limitations before using the result.
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