Radiation Dose Converter

Frequently Asked Questions

What is the difference between gray and sievert?

Gray (Gy) is absorbed dose - energy deposited per kg. Sievert (Sv) is equivalent dose - Gy weighted for biological harm by radiation type. They are NOT interchangeable; the tool keeps them in separate modes.

How do rad and rem convert?

1 Gy = 100 rad (absorbed); 1 Sv = 100 rem (equivalent). Older US references use rad/rem; SI uses Gy/Sv.

Why can't I convert Gy directly to Sv?

It requires a radiation weighting factor (1 for X/gamma/beta, up to 20 for alpha). Only for those wR=1 cases are the numbers equal - hence separate modes.

What are reference doses?

A chest X-ray ≈ 0.1 mSv, annual background ≈ 3 mSv, a CT scan ≈ 7 mSv. This converter is educational, not a dosimetry or medical tool.

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Estimates for informational purposes only.

Important Disclaimer: Estimates for informational purposes only.

This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

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How This Calculator Works

Radiation dose comes in two distinct families, kept in separate modes here because they must never be cross-converted. Absorbed dose is the energy deposited per unit mass of tissue; its SI base unit is the gray (Gy), defined as one joule per kilogram. Equivalent dose is absorbed dose multiplied by a dimensionless radiation weighting factor that reflects how biologically damaging the radiation type is; its SI base unit is the sievert (Sv). Within each mode every unit is a fixed multiple of the base, so conversion pivots through it: result = amount × (basePerFrom ÷ basePerTo). The legacy CGS units are exact decimal multiples: 1 rad = 0.01 Gy and 1 rem = 0.01 Sv. The SI prefixes follow: 1 mGy = 0.001 Gy, 1 µGy = 10−6 Gy, and likewise for mSv and µSv. This is an educational tool - for clinical or regulatory decisions consult a qualified medical physicist.

Worked Example

A study reports a 250 mrem effective dose and you want sieverts. First convert mrem to rem: 250 mrem = 0.25 rem. Step 1: 0.25 × 0.01 = 0.0025 Sv. Step 2: 0.0025 ÷ 0.001 = 2.5 mSv - roughly a year of natural background. Absorbed-dose example: a radiotherapy fraction of 200 rad equals 200 × 0.01 = 2 Gy. Reverse it: 0.1 Gy is 0.1 ÷ 0.01 = 10 rad, or 100 mGy.

Why Gy and Sv Differ

For X-rays, gamma rays, and beta particles the radiation weighting factor is 1, so 1 Gy happens to equal 1 Sv numerically - but they are still different physical quantities. For alpha particles the weighting factor is about 20, so 1 Gy of alpha exposure is roughly 20 Sv of equivalent dose. Because that factor depends on radiation type (and is outside this calculator's scope), the tool deliberately blocks converting gray to sievert. Pick the mode that matches the quantity you actually have.

Common Mistakes

Cross-converting Gy and Sv: never multiply or divide gray by a fixed number to get sievert - the weighting factor depends on radiation type.

rad vs rem: both are 0.01 of their SI unit, but rad is absorbed dose and rem is equivalent dose - not interchangeable.

Prefix slips: mSv to µSv is ×1000; a misplaced prefix turns a routine scan into an alarming number.

Dose vs dose rate: Sv is a total dose; Sv per hour is a rate. This tool converts the dose, not exposure time.

Effective vs equivalent dose: both are in sieverts but apply different tissue factors; the unit alone does not tell you which.

Radiation Dose Converter

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