Workplace radon dose calculator

Use this calculator to estimate a worker’s annual effective dose from exposure to radon-222 (Rn-222) and its short-lived decay products. The estimate is based on the radon concentration in the area, the time the worker spends there and the equilibrium factor used.

The calculator defaults to ICRP Publication 65. You can instead select ICRP Publication 137 or compare the results produced by both methods. The appropriate calculation method depends on the purpose of the assessment and the arrangements under which the result will be used. Where the calculation may support a statutory dose record or a formal regulatory decision, confirm the method with the appointed Radiation Protection Adviser or approved dosimetry service.

Radon concentration can be entered in Bq/m³ or pCi/L. Where pCi/L is selected, the value is converted internally using 1 pCi/L = 37 Bq/m³, and all dose calculations are then completed using Bq/m³.

Before using the calculator

Enter a radon concentration that is representative of the worker’s exposure while they are in the area. Enter only the hours spent at that concentration, rather than the worker’s total employment hours unless the stated concentration applies throughout all working time.

The calculator suggests an equilibrium factor of F = 0.4. Only use another value where it has been measured or professionally justified.

Scope: This calculator covers radon-222 and its short-lived progeny only. It does not calculate dose from radon-220 (thoron) or thoron progeny. Do not enter an uncorrected combined radon/thoron measurement.

Uses the ICRP Publication 65 occupational dose conversion factor of 3.2 × 10⁻⁶ mSv per Bq·h·m⁻³ at F = 0.4, adjusted for the selected equilibrium factor.

Choose the concentration unit
Bq·m⁻³

Enter the average radon-222 concentration that applies while the worker is in this area. Do not enter a radon-220 (thoron) result or an uncorrected combined radon/thoron result.

All calculations are performed in Bq·m⁻³. Select pCi/L where that is how the measurement was reported.

Choose a typical occupancy or enter a more accurate annual exposure time below.

hours/year

Enter only the time spent at the radon concentration stated above. Maximum: 8,760 hours/year.

F

Suggested default for radon-222: F = 0.4. Only use another value where it has been measured or professionally justified. Do not use this radon-222 default as a thoron equilibrium factor.

How the calculation works

The calculator first determines the radon exposure:

Radon exposure = radon-222 concentration × exposure time

For the selected calculation method, it then uses a reference dose conversion factor stated at an equilibrium factor of F = 0.4. That reference factor is adjusted for the equilibrium factor entered by the user:

Adjusted dose conversion factor = reference dose conversion factor × (selected F ÷ 0.4)

The annual effective dose is then calculated as:

Effective dose = radon-222 concentration × exposure time × adjusted dose conversion factor

ICRP Publication 65

For this option, the calculator uses a reference occupational dose conversion factor of:

3.2 × 10⁻⁶ mSv per Bq·h·m⁻³ at F = 0.4

The factor is adjusted in direct proportion to the selected equilibrium factor. For example, at F = 0.5 the adjusted factor is:

3.2 × 10⁻⁶ × (0.5 ÷ 0.4) = 4.0 × 10⁻⁶ mSv per Bq·h·m⁻³

ICRP Publication 137

At F = 0.4, the calculator uses:

  • 6.7 × 10⁻⁶ mSv per Bq·h·m⁻³ for most workplace circumstances; or
  • 13.4 × 10⁻⁶ mSv per Bq·h·m⁻³ for indoor work involving substantial physical activity or for tourist-cave work.

The higher coefficient should not be selected solely because a task includes some manual work. It is intended for the specific exposure circumstances described by ICRP. Seek specialist advice where the appropriate category is uncertain.

Breathing rate and physical activity

The amount of radon progeny inhaled can increase as breathing rate rises, for example during strenuous work. This calculator does not apply a separate user-entered breathing-rate adjustment and should not be interpreted as worker-specific respiratory dosimetry.

Where a worker experiences several activity levels, moves between areas with different concentrations or equilibrium factors, or requires a custom breathing-rate assessment, use the Advanced Radon Exposure Profile Calculator or obtain specialist advice.

Radon-220 (thoron)

Radon-220 and its progeny are not included. Thoron has a short half-life of approximately 56 seconds, so concentrations can vary sharply with distance from the emitting surface and thoron gas may be far from equilibrium with its progeny. The radon-222 default of F = 0.4 should not be applied to thoron.

Where thoron could make a material contribution, use measurement equipment capable of distinguishing radon-222 from thoron and arrange a separate assessment based on appropriate thoron or thoron-progeny measurements. If an instrument has known thoron interference, enter only the corrected radon-222 result in this calculator.

Interpreting the result

This calculator provides an indicative estimate. Its reliability depends on the entered concentration, equilibrium factor and occupancy being representative of the worker’s exposure. It does not replace a suitable and sufficient radiation risk assessment, representative workplace measurements or advice from a suitable Radiation Protection Adviser.

If a representative annual-average concentration in an occupied workplace exceeds 300 Bq·m⁻³, the employer must notify HSE under the Ionising Radiations Regulations 2017. An RPA with suitable radon experience should normally be consulted. A calculated dose should not be used by itself to decide whether IRR17 applies, whether an area requires designation or whether a worker requires classification.

References and calculation basis

Calculator version: 2.2
Calculation basis reviewed: July 2026