Why can't I convert Bq to Gy without a dose coefficient?

Becquerels count disintegrations per second but say nothing about energy deposition. A single disintegration from different isotopes releases vastly different energy amounts. The dose coefficient (Gy/Bq) bridges the gap and depends on the specific isotope, radiation type, tissue, and intake pathway.

Where do I find the dose coefficient for my isotope?

The ICRP (International Commission on Radiological Protection) publishes dose coefficients in its publication series (e.g., ICRP-72 for ingestion/inhalation). The US EPA and NRC also publish tabulations. Look up your radionuclide, exposure pathway (ingestion, inhalation, external), and target organ.

What is one gray equal to?

One gray (Gy) equals one joule of energy absorbed per kilogram of matter (1 J/kg). It replaces the older unit rad (1 Gy = 100 rad).

Is gray the same as sievert?

No. Grays measure absorbed dose (physical energy deposition). Sieverts measure effective dose, which weights absorbed dose by the biological effectiveness of the radiation type and the sensitivity of the tissue. For gamma and X-ray radiation the weighting factor is 1, so Gy and Sv are numerically equal, but they measure different things.

What is a typical dose coefficient for a common isotope?

As an example, the effective dose coefficient for oral ingestion of I-131 is approximately 2.2 × 10⁻⁸ Sv/Bq (ICRP-72). Absorbed dose coefficients in Gy/Bq vary by organ and isotope; always consult authoritative tables for your specific case.

Becquerel to Gray Converter

Name: Becquerel to Gray Converter
Availability: InStock
Author: Nham Vu

Enter activity in becquerels and a dose coefficient to calculate absorbed dose in grays.

Inputs

Absorbed dose (Gy) = Activity (Bq) × Dose coefficient (Gy/Bq)

Activity

Select a unit; the value is converted to Bq internally.

Dose coefficient (Gy/Bq)

From ICRP / EPA tables for your specific isotope, pathway, and tissue.

Quick examples

Results

Enter values and press Calculate

Bq vs. Gy — what the units actually mean

Becquerel (Bq)

One becquerel is one radioactive disintegration per second. It describes how active a source is, not how much energy it deposits. A source can be highly active but deliver a negligible dose if its emissions are weakly penetrating or quickly stopped.

Gray (Gy)

One gray is one joule of energy absorbed per kilogram of tissue (1 J/kg). It describes the biological target, not the source. The link between the two quantities — the dose coefficient — encodes everything about the isotope's decay energy, radiation type, and how it travels through or accumulates in tissue.

Summary

Enter activity in becquerels and a dose coefficient to calculate absorbed dose in grays.

How it works

Enter the activity in becquerels (Bq) — this is the quantity of radioactive material.
Enter the dose coefficient in Gy/Bq for your specific radionuclide and tissue combination.
The tool multiplies activity × dose coefficient to give absorbed dose in grays (Gy).
Results are also shown in milligrays (mGy) and micrograys (µGy) for convenience.
Use published tables (ICRP, EPA) to find the correct dose coefficient for your scenario.

Use cases

Radiation protection calculations for known radionuclide intake.
Medical physics dosimetry for internally deposited radiopharmaceuticals.
Educational exploration of the Bq→Gy relationship.
Cross-checking hand calculations in nuclear safety reviews.
Environmental dose assessment using published dose coefficients.

Frequently Asked Questions

Last updated: 2026-07-22 · Reviewed by Nham Vu