Radioactivity mass concentration unit converter

This radioactivity mass concentration converter allows users to convert between commonly used activity concentration by mass units, including SI becquerel-based quantities and legacy curie-based quantities that continue to appear in historical records, international guidance, waste documentation, environmental reporting, and training materials.

It is intended to support clear communication, sense-checking of values, and consistent interpretation of mass-based activity concentration across different regulatory, technical, and educational contexts.

What this calculator does

Radioactivity (activity) describes the rate of radioactive decay. When that activity is expressed per unit mass, it becomes a mass activity concentration (for example, Bq/kg), which is widely used for:

  • waste characterisation and clearance / exemption assessments (where applicable);

  • environmental sampling results (soil, sediment, biota, building materials);

  • NORM/TENORM assessments and contaminated materials;

  • technical reporting, comparison of datasets, and training.

In UK and international practice, mass activity concentration is typically expressed using Bq/kg (and sub-multiples or multiples such as mBq/kg, kBq/kg, MBq/kg). However, legacy units such as pCi/g and related curie-based expressions are still encountered, particularly in older documentation and some non-UK publications.

This calculator provides straightforward conversion between mass activity concentration units using accepted, fixed relationships for both:

  • activity units (Bq and Ci families), and

  • mass units (microgram, milligram, gram, kilogram, tonne).

Supported mass concentration units

The calculator supports conversion between the following mass activity concentration units:

SI units (becquerel-based)

Per microgram (µg)

  • millibecquerels per microgram (mBq/µg)

  • becquerels per microgram (Bq/µg)

  • kilobecquerels per microgram (kBq/µg)

  • megabecquerels per microgram (MBq/µg)

  • gigabecquerels per microgram (GBq/µg)

  • terabecquerels per microgram (TBq/µg)

Per milligram (mg)

  • millibecquerels per milligram (mBq/mg)

  • becquerels per milligram (Bq/mg)

  • kilobecquerels per milligram (kBq/mg)

  • megabecquerels per milligram (MBq/mg)

  • gigabecquerels per milligram (GBq/mg)

  • terabecquerels per milligram (TBq/mg)

Per gram (g)

  • millibecquerels per gram (mBq/g)

  • becquerels per gram (Bq/g)

  • kilobecquerels per gram (kBq/g)

  • megabecquerels per gram (MBq/g)

  • gigabecquerels per gram (GBq/g)

  • terabecquerels per gram (TBq/g)

Per kilogram (kg)

  • millibecquerels per kilogram (mBq/kg)

  • becquerels per kilogram (Bq/kg)

  • kilobecquerels per kilogram (kBq/kg)

  • megabecquerels per kilogram (MBq/kg)

  • gigabecquerels per kilogram (GBq/kg)

  • terabecquerels per kilogram (TBq/kg)

Per tonne (t)

  • millibecquerels per tonne (mBq/t)

  • becquerels per tonne (Bq/t)

  • kilobecquerels per tonne (kBq/t)

  • megabecquerels per tonne (MBq/t)

  • gigabecquerels per tonne (GBq/t)

  • terabecquerels per tonne (TBq/t)

Legacy units (curie-based)

Per microgram (µg)

  • picocuries per microgram (pCi/µg)

  • nanocuries per microgram (nCi/µg)

  • microcuries per microgram (µCi/µg)

  • millicuries per microgram (mCi/µg)

  • curies per microgram (Ci/µg)

  • kilocuries per microgram (kCi/µg)

Per milligram (mg)

  • picocuries per milligram (pCi/mg)

  • nanocuries per milligram (nCi/mg)

  • microcuries per milligram (µCi/mg)

  • millicuries per milligram (mCi/mg)

  • curies per milligram (Ci/mg)

  • kilocuries per milligram (kCi/mg)

Per gram (g)

  • picocuries per gram (pCi/g)

  • nanocuries per gram (nCi/g)

  • microcuries per gram (µCi/g)

  • millicuries per gram (mCi/g)

  • curies per gram (Ci/g)

  • kilocuries per gram (kCi/g)

Per kilogram (kg)

  • picocuries per kilogram (pCi/kg)

  • nanocuries per kilogram (nCi/kg)

  • microcuries per kilogram (µCi/kg)

  • millicuries per kilogram (mCi/kg)

  • curies per kilogram (Ci/kg)

  • kilocuries per kilogram (kCi/kg)

Per tonne (t)

  • picocuries per tonne (pCi/t)

  • nanocuries per tonne (nCi/t)

  • microcuries per tonne (µCi/t)

  • millicuries per tonne (mCi/t)

  • curies per tonne (Ci/t)

  • kilocuries per tonne (kCi/t)

Conversion basis

Conversions are based on the standard relationship:

1 Ci = 3.7 × 10¹⁰ Bq

Mass conversions are based on standard metric relationships:

  • 1 mg = 1,000 µg

  • 1 g = 1,000 mg

  • 1 kg = 1,000 g

  • 1 t = 1,000 kg

Important note on tonnes (UK metric tonne)

This calculator uses the metric tonne, abbreviated t, which is the standard unit in the UK and is defined as:

1 t = 1,000 kg

It does not use US customary “tons” (short ton) or imperial tons. In US contexts, “ton” may refer to:

  • short ton (often written “ton” or “tn”): approximately 907.18 kg, or

  • imperial ton: approximately 1,016.05 kg.

To avoid ambiguity and ensure consistent, defensible calculations, all conversions in this calculator that use “t” are based only on the UK metric tonne definition (1,000 kg).

Appropriate use

This calculator is suitable for use when:

  • reviewing waste documentation, sampling reports, or inventories that use different mass-based activity units;

  • interpreting international publications where curie-based mass concentrations (e.g. pCi/g or pCi/µg) are used;

  • converting values for communication or comparison purposes;

  • supporting education and professional development activities.

It is not intended to replace radionuclide characterisation, laboratory reporting requirements, regulatory submissions, or waste acceptance decisions where additional information (e.g. radionuclide, measurement basis, uncertainty, sampling method) is required.

Important note

The results provided by this calculator are indicative only and assume idealised unit relationships. They do not account for uncertainty, measurement methodology, decay since reference time, radionuclide mix, or sampling representativeness.

Outputs should not be relied upon as the sole basis for compliance decisions, waste classification, clearance determinations, or safety justifications. Where required, advice should be sought from a competent Radiation Protection Adviser (RPA), Radioactive Waste Adviser (RWA) or other suitably qualified professional.

Related guidance

Activity concentration quantities and units are discussed within internationally recognised metrology and radiological protection guidance, including publications from authoritative standards bodies. These concepts are implemented within UK legislative and regulatory frameworks across sectors such as nuclear, environmental protection, medical, industrial, research, and transport.

Users should ensure that activity concentration values are interpreted within their correct regulatory, measurement, and exposure context.

For advice on applying activity concentration information within your organisation or regulatory framework, please contact RP Alba Ltd.