Radiological calculators
RP Alba Ltd provides a growing suite of radiological calculators to support practitioners, duty holders, and others working with ionising radiation. These tools are intended to aid understanding, sense-checking, and professional communication across a range of radiation protection and radioactive waste management contexts.
The calculators are designed to be clear, transparent, and technically correct, reflecting current UK practice and internationally recognised radiological quantities and units.
Purpose and scope
The calculators provided in this section are suitable for use in a wide range of settings, including:
occupational radiation protection;
transport of radioactive material;
environmental and public exposure contexts;
training, education, and professional development.
They are intended to support informed decision-making and discussion but do not replace site-specific risk assessments, local rules, or advice from a competent Radiation Protection Adviser (RPA) or Radioactive Waste Adviser (RWA).
Each calculator is accompanied by explanatory notes to help users understand both the calculation and its appropriate limitations.
Available calculators
Radioactivity unit converter
Convert between commonly used radioactivity (activity) units, including SI becquerel-based quantities and legacy curie-based units.
This calculator supports conversion between units such as:
- Bq, kBq, MBq, GBq, TBq, PBq
- pCi, nCi, µCi, mCi, Ci, kCi, MCi.
Radioactivity mass concentration unit converter
Convert between commonly used radioactivity mass concentration units, including SI becquerel-based and legacy curie-based expressions.
This calculator supports conversion between units such as:
- Bq/kg, mBq/kg, kBq/kg, MBq/kg (and equivalents per µg, mg, g, and tonne)
- pCi/g, nCi/g, µCi/g (and equivalents per µg, mg, kg, and tonne).
Radioactivity volume concentration unit converter
Convert between commonly used radioactivity volume concentration units, including SI becquerel-based and legacy curie-based expressions.
This calculator supports conversion between units such as:
- Bq/m³, Bq/L, Bq/mL (and their milli-, kilo-, mega-, and giga-sub-multiples)
- pCi/L, pCi/m³, pCi/mL (and related curie-based units).
Radon concentration unit converter
Convert between the two most commonly used units for radon gas concentration in air.
This calculator supports conversion between:
- Bq/m³ (and kBq/m³) and pCi/L.
Radioactivity calculator (mass to activity)
Estimate the radioactive activity of a material from a known mass of a single radionuclide.
This calculator uses authoritative radionuclide data (including half-life and atomic mass) to apply the radionuclide’s specific activity and determine the resulting activity in units such as Bq, kBq, MBq, GBq, or curie-based equivalents.
Radioactivity calculator (activity to mass)
Estimate the mass of a radioactive material from a known activity for a single radionuclide.
This calculator applies authoritative radionuclide data (including half-life and atomic mass) to determine the mass corresponding to a specified activity, expressed in units such as grams, milligrams, kilograms, or tonnes.
Radioactive decay calculator (defined elapsed time period)
Estimate the remaining activity of a single radionuclide after a defined period of radioactive decay.
This calculator uses authoritative half-life data to determine how activity reduces over time and presents the remaining activity alongside the fraction remaining and the number of half-lives elapsed. It is particularly useful for decay-in-storage assessments, transport and waste planning, and regulatory sense-checking.
Radioactive decay calculator (specified dates)
Calculate the remaining activity of a single radionuclide between two specified dates and times.
This calculator is particularly useful where radioactive material is received, handled, or assessed at known points in time, such as in nuclear medicine, transport planning, or compliance checks against permit or licence limits. Results include the remaining activity, fraction remaining, and number of half-lives elapsed.
Radioactive decay calculator (time to reach target activity)
Calculate the time required for a single radionuclide to decay from a known initial activity to a specified target activity.
This calculator is particularly useful for decay-in-storage planning, waste management, and compliance assessments where material must be held until activity falls below a defined threshold. Results include the time required, the fraction of activity remaining, and the number of half-lives that need to have elapsed.
Radioactive decay calculator (date/time to reach target activity)
Estimate the calendar date and time at which a single radionuclide will decay from a known initial activity to a specified target activity.
This calculator is particularly useful for planning decay-in-storage, nuclear medicine operations, and compliance checks where activity limits must be met by a defined date and time. Results include the target date/time, the fraction of activity remaining, and the number of half-lives that need to have elapsed.
Effective dose unit converter
Convert between commonly used radiation dose units, including sievert-based and rem-based quantities.
This calculator supports conversion between units such as:
sievert (Sv), millisievert (mSv), microsievert (µSv), nanosievert (nSv)
rem, millirem (mrem), microrem (µrem).
Effective dose rate unit converter
Convert between commonly used effective dose rate units, including sievert-based and rem-based quantities expressed per second, per minute, or per hour.
This calculator supports conversion between units such as:
- µSv/hr, µSv/min, µSv/sec; mSv/hr, mSv/min, mSv/sec; Sv/hr, Sv/min, Sv/sec
- µrem/hr, µrem/min, µrem/sec; mrem/hr, mrem/min, mrem/sec; rem/hr, rem/min, rem/sec.
Absorbed dose unit converter
Convert between commonly used absorbed dose units, including gray-based and rad-based quantities.
This calculator supports conversion between units such as:
- gray (Gy), milligray (mGy), microgray (µGy), nanogray (nGy)
- rad, millirad (mrad), microrad (µrad).
Absorbed dose rate unit converter
Convert between commonly used absorbed dose rate units, including gray-based and rad-based quantities expressed per second, per minute, or per hour.
This calculator supports conversion between units such as:
- µGy/hr, µGy/min, µGy/sec; mGy/hr, mGy/min, mGy/sec; Gy/hr, Gy/min, Gy/sec
- µrad/hr, µrad/min, µrad/sec; mrad/hr, mrad/min, mrad/sec; rad/hr, rad/min, rad/sec.
Inverse square law dose rate calculator (dose rate at a new distance)
Estimate how radiation dose rate changes with distance using the inverse square law.
This calculator allows you to calculate the dose rate at a new distance based on a known dose rate at a reference distance, with support for common distance units (mm, cm, m, in, ft, yd) and dose-rate units (Sv/hr and rem-based equivalents).
It is particularly useful for stand-off distance planning, training, and quick sense-checking in radiation protection scenarios where point-source behaviour can be assumed.
Inverse square law distance calculator (distance required to achieve a target dose rate)
Estimate the distance required to achieve a specified radiation dose rate using the inverse square law.
This calculator allows users to determine the distance at which a target dose rate would occur, based on a known dose rate at a reference distance. It supports commonly used distance units and dose-rate units, including sievert-based and rem-based quantities.
It is particularly useful for stand-off distance planning, task design, and training scenarios where point-source, far-field behaviour can be assumed, and for sense-checking the effect of distance on radiation exposure.
External radiation dose estimator
Estimate total external effective dose from a known dose rate and exposure duration. Supports SI and legacy units (e.g. rem), selectable time units (seconds to years), optional occupancy factor, and scalable outputs (nSv to Sv and rem-based equivalents). Useful for non-destructive testing (NDT) work planning and for annualising low environmental dose rates (e.g. nSv/hr × 1 year) to support consideration of area designations and permit-related sense checks.
Maximum stay time estimator
Estimate the maximum allowable exposure time for a given external radiation dose rate and target dose. This calculator supports common SI and legacy units (rem), selectable time units (seconds to years), and an optional occupancy factor, with results presented in both a chosen unit and a practical “friendly” time breakdown.
It is particularly useful for NDT and industrial radiography work planning, task briefings, and controlled area management, where clear stay-time limits are required to keep doses within defined constraints.
Transport Index (TI) calculator
Calculate the Transport Index (TI) for a radioactive package based on the maximum external dose rate measured at 1 metre from the package surface. The calculator supports common SI and legacy dose-rate units, applies the standard transport calculation and rounds the result up to one decimal place, with TI values of 0.05 or less treated as zero.
This tool is intended to support Class 7 transport activities, including preparation and review of transport documentation, and highlights cases where a high TI (>10) indicates the need for additional consultation with a DGSA and/or RPA.
Dose rate at 1 m calculated from Transport Index
Estimate the radiation dose rate at 1 metre from a package based on a stated Transport Index (TI). This calculator converts a dimensionless TI value into a corresponding external dose rate using standard transport relationships, with results shown in common SI and legacy units.
It is useful when reviewing transport documentation, planning work around packages with known TI values, or as a sense-check before estimating dose rates at other distances using inverse square calculations.
Radon calculators
RP Alba Ltd provides four radon calculators covering workplace exposure, exposure of members of the public, complex multi-location exposure profiles, and ingestion of radon in drinking water.
Select the calculator that most closely matches the exposure pathway and circumstances being assessed. Each tool includes explanatory notes, calculation details and important limitations to help users understand how the result has been derived.
Workplace radon dose calculator
Estimate a worker’s annual effective dose from exposure to radon-222 and its short-lived decay products in a workplace.
The calculator uses the average radon concentration, annual exposure time and equilibrium factor. It allows users to apply ICRP Publication 65, ICRP Publication 137, or compare both methods. It is most suitable where the worker is exposed at one representative concentration and equilibrium factor.
Home and public radon dose calculator
Estimate the annual effective dose received by a member of the public from radon-222 exposure in a home, school or other building.
The calculator includes suggested occupancy assumptions for adults, children, pupils, students and visitors. It allows users to apply ICRP Publication 65, ICRP Publication 158, or compare both methods. People exposed as part of their work should use the workplace calculator instead.
Advanced radon exposure profile calculator
Estimate a person’s combined annual effective dose where exposure occurs across several locations, tasks or time periods.
Each exposure scenario can use a different radon concentration, annual exposure time and equilibrium factor. Worker and public calculation methods are available, together with an optional hypothetical breathing-rate sensitivity calculation for applicable worker scenarios. All exposure periods are added together as one annual profile.
Radon in drinking water ingestion dose calculator
Estimate the committed effective dose from ingesting radon-222 dissolved in drinking water.
The calculation uses the radon concentration in the water, the annual volume consumed and the applicable ingestion dose coefficient. It includes the ICRP Publication 137 adult Reference Worker coefficient and the age-dependent public coefficients from ICRP Publication 158. The result covers ingestion only and does not estimate inhalation exposure from radon released into indoor air.
Other calculators
Additional radiological calculators will be added to this section over time. If there is a specific calculator that you would like us to consider adding then please get in contact and we will give it consideration.
If you would like to discuss how these tools apply to your organisation or require tailored advice, please contact RP Alba Ltd.
Important note
The outputs from these calculators are indicative only. They are based on standard definitions and assumptions and should not be relied upon as the sole basis for regulatory compliance, dose restriction decisions, or formal safety assessments.
Where required, professional judgement and competent advice should always be sought.