This page brings together a range of practical radiation-related calculators and conversion tools to support day-to-day work, training, and quick reference use. These tools are intended to assist users with common calculations, including decay and time-based estimations, in a simple and accessible format.
About these tools
The calculators on this page have been developed to provide a convenient starting point for routine radiation-related calculations. ARPS will continue to refine and expand these tools over time to improve usability and consistency across the page.
Feedback is welcome. If you identify an issue, unexpected result, or improvement opportunity, please contact ARPS so the calculators can be reviewed and updated where needed - Matthew Wiggins.
Disclaimer
These calculators are provided as general tools only and should be used with professional judgement. Users are responsible for independently verifying inputs, assumptions, units, and results before relying on them for operational, regulatory, clinical, research, safety, or decision-making purposes. ARPS does not guarantee that the calculators are free from error and accepts no responsibility for outcomes arising from their use.
Decay calculator
Calculate the remaining activity after decay using the selected isotope half-life. You can either enter a time elapsed directly or calculate it from a start and end date/time. The decay factor is unitless, so the result stays in the same activity unit you entered.
This only filters the isotope list below.
Half-life values in the dropdown are stored in days.
Use any consistent activity unit here. The result will be returned in the same unit.
Date and time entries use the browser’s local timezone.
Results
Remaining activity (same unit as input)
—
Decay factor
—
Elapsed time used
—
Selected isotope
—
Enter an isotope, activity, and either an elapsed time or two date/time values to calculate the remaining activity.
Activity Converter
Convert activity values between becquerel and curie-based units.
Enter the activity and choose the starting unit.
Results
Converted value
—
Conversion
—
Enter a value and select the units to convert the activity.
Inverse Square Law Calculator
Calculate intensity change with distance using the inverse square law.
Use the same unit selection for both distances.
The calculator preserves whatever units you use for intensity.
Results
End intensity
—
Intensity factor
—
Enter the starting distance, end distance, and initial intensity to calculate the new intensity.
Because this uses a ratio of distances squared, the chosen distance units cancel out as long as both distances use the same unit. The output remains in the same intensity unit as the input.
Radon Curie / Becquerel Converter
Convert radon concentration between Ci/L and Bq/m³.
Example: 1 pCi/L = 37 Bq/m³.
This calculator uses the standard relationship of 1 Ci/L = 3.7 × 1013 Bq/m³, so 1 pCi/L = 37 Bq/m³.
Radiation Shield Calculator
Calculate the transmitted activity or intensity after passing through a shield using exponential attenuation.
Use any consistent activity or intensity unit. The transmitted result will be returned in that same unit.
Use units of cm⁻¹.
Results
Transmitted activity / intensity
—
Transmission fraction
—
Attenuation
—
Enter the initial value, shield thickness, and linear attenuation coefficient to calculate the transmitted value.
This calculator uses exponential attenuation and assumes the attenuation coefficient and thickness are compatible. Thickness is converted internally to cm for use with μ in cm⁻¹.
Time calculator
Calculate how long it will take for an isotope to decay from an original activity to a target activity. You can return the result as an elapsed time, or enter a start date and time to calculate the projected end date and time.
This only filters the isotope list below.
Half-life values in the dropdown are stored in days.
Use any activity unit, as long as both activity values use the same one.
Used only when calculating an end date and time. This uses the browser’s local timezone.
Results
Time to decay
—
Equivalent half-lives
—
Projected end date and time
—
Selected isotope
—
Enter an isotope, original activity, and target activity to calculate the required decay time.
Because this calculation uses the ratio between the original and target activities, the activity unit cancels out. That makes the calculator flexible for Bq, kBq, MBq, Ci, mCi, or any other consistent unit pair.
Radon Sensitivity Unit Converter
Convert radon detector sensitivity values expressed as count rate per activity concentration, such as CPM/pCi/L and CPS/kBq/m³. This is useful for comparing instruments, specifications, and calibration-style sensitivity values across different radon units.
Example: CPM / pCi / L means counts per minute per pCi/L.
Results
Unit 1 definition
—
Unit 2 definition
—
Status
Enter a value in either Unit 1 or Unit 2 to convert.
This calculator converts sensitivity values normalised to activity concentration. It is most useful for radon monitor specifications, comparison tables, and instrument sensitivity conversions.
Roentgen Converter
Convert roentgen values to coulombs per kilogram and estimate absorbed dose in grays for the selected medium, using commonly referenced air and tissue conversion factors.
Enter the roentgen value and choose the prefix scale.
The gray conversion factor depends on the selected medium.
Results
C/kg
—
Grays
—
Medium
—
Enter a roentgen value to calculate the equivalent C/kg and grays.
This calculator provides an exposure conversion and an approximate absorbed dose estimate for the selected medium. It is most useful as a quick reference tool rather than a full dosimetric assessment.
Uranium / Plutonium / Actinide Grams Calculator
Convert between activity and mass for selected long-lived isotopes. This calculator is useful when you need a quick estimate of how much material corresponds to a given activity, or the reverse, for single isotopes or simple mixtures.
Totals
Total activity
—
Total mass
—
Status
Enter one or more isotope values to calculate.
This version uses the isotope mass number as the molar-mass approximation in the activity–mass relationship, which is generally suitable for practical estimation.