External radiation dose estimator

This calculator estimates the total effective dose received from a known external radiation dose rate over a specified duration. It is intended to support radiation protection practitioners with quick, dimensionally correct calculations for work planning, sense-checking, and communication of dose implications.

The calculator normalises time internally to hours and applies straightforward unit conversions between SI and legacy dose units.

Looking for the inverse calculation?

If you need to determine the maximum time that a person can remain in an area for a given target dose, use the maximum stay time estimator.

Maximum stay time estimator

What the calculator on this page does

Given:

  • an effective dose rate (\(\dot{E}\)), and
  • an exposure duration (\(t\)),

the external radiation dose estimator calculates total effective dose (\(E\)) using:

\(E = \dot{E} \times t\)

An optional occupancy factor may be applied where exposure is intermittent or where time-at-risk is a defined fraction of a period.

Supported radiation dose rate units

The calculator supports common effective dose rate units used in radiation protection, including SI units and legacy units that still appear in historical documentation and international sources:

  • nanosieverts per hour (nSv/hr)

  • microsieverts per hour (µSv/hr)

  • millisieverts per hour (mSv/hr)

  • sieverts per hour (Sv/hr)

  • microrem per hour (µrem/hr)

  • millirem per hour (mrem/hr)

  • rem per hour (rem/hr)

Conversions use the standard relationship:

  • 1 Sv = 100 rem

Supported exposure duration units

Exposure duration can be entered in:

  • seconds (s)

  • minutes (min)

  • hours (hr)

  • days (d)

  • years (yr)

For annualisation calculations, the calculator uses:

  • 1 year = 365.24 days

This supports common environmental and monitoring applications where dose rate measurements (often in nSv/hr) are used to estimate potential annual dose.

Output units

Total dose outputs are unit-scalable and can be displayed in a user-selected unit. Output options include:

  • nSv, µSv, mSv (default), Sv

  • µrem, mrem, rem

This helps users present results in the most appropriate unit for reporting, comparison, or communication.

Appropriate use

This calculator is suitable for:

  • estimating dose received during a task when a representative dose rate is known;

  • comparing alternative working durations and stand-off arrangements;

  • supporting education and professional development;

  • annualising low environmental dose rates (e.g., nSv/hr × 1 year) for monitoring interpretation.

It can also assist with preliminary sense-checking against UK area designation thresholds under the Ionising Radiations Regulations, for example:

  • Potential for >1 mSv in a year may indicate the need for a supervised area; 

  • Potential for >6 mSv in a year may indicate the need for a controlled area.

These comparisons should be used as an aid to judgement rather than as a standalone decision rule. A suitable appointed Radiation Protection Adviser (RPA) must always be consulted when deciding whether to designated an area as supervised or controlled under the UK’s Ionising Radiations Regulations.

Important note

Results are indicative and assume:

  • the dose rate is representative of the exposure period,

  • conditions remain stable (no change in source strength, shielding, distance, or occupancy),

  • and the input dose rate already reflects the appropriate quantity (effective external radiation dose rate).

This calculator does not replace formal dose assessment, personal dosimetry, workplace monitoring strategies, or regulatory submissions. Where required, advice should be sought from a competent Radiation Protection Adviser (RPA) or other suitably qualified professional.