Verification: factors follow standard unit definitions; round for display only.

Gray to sievert

Convert Gy to Sv when a radiotherapy physics report, dosimeter calibration sheet, or research dataset lists absorbed dose in gray but radiation protection summaries, effective dose records, or ICRP-style risk tables quote sieverts.

The gray (Gy) is the SI unit of absorbed dose: energy deposited per unit mass (1 Gy = 1 J/kg). The sievert (Sv) is the SI unit of dose equivalent (and, with tissue weighting, effective dose): absorbed dose multiplied by radiation weighting factors that reflect biological effectiveness. Under this site's radiation catalog both units share the same numeric anchor (Gray = 1, Sievert = 1), but they measure related—not identical—quantities.

For photons (X-rays, gamma) and most electrons: H = D × Q where Q = 1 → 1 Gy = 1 Sv numerically

When the radiation weighting factor Q (formerly quality factor) equals 1, equivalent dose in sieverts matches absorbed dose in gray at the same point. For neutrons, protons, or alpha particles, Q can be much larger—1 Gy absorbed may correspond to many sieverts equivalent. Always confirm radiation type before equating units.

Step-by-step conversion (worked example — 2 Gy photon beam)

A radiotherapy fraction delivers 2 Gy to a tumor with megavoltage photons (Q ≈ 1):

1. Confirm radiation type: photon beam → Q = 1 for protection-style equivalence
2. Equivalent dose H = D × Q = 2 × 1 = 2 Sv at that point (numerically)
3. Note: treatment planning still reports tumor dose in Gy; whole-body effective dose to staff uses Sv with geometry and tissue weighting

Second worked example (0.05 Gy environmental photon field)

An environmental survey reads 0.05 Gy absorbed in tissue-equivalent material from gamma:

1. Q = 1 for photons → 0.05 Sv equivalent dose (same number)
2. Convert for public communication: 0.05 Sv = 50 mSv via sievert to millisievert

Third worked example (1 Gy neutron — when numbers diverge)

The same 1 Gy absorbed from fast neutrons might use Q ≈ 10–20 depending on energy:

1. H = 1 Gy × Q → 10–20 Sv equivalent (not 1 Sv)
2. Lesson: Gy→Sv is not always 1:1—photon/electron cases are the common equal-numeric exception

Gray to sievert reference table (Q = 1 photon/electron case)

Where gray → sievert comes up

• Medical imaging: CTDIvol and similar metrics report absorbed dose in mGy; patient effective dose summaries may appear in mSv after organ weighting—not a simple mGy→mSv prefix swap without coefficients.
• Radiotherapy: Prescriptions state Gy to target; occupational dosimeters for staff track Sv for whole-body exposure.
• Occupational health physics: Area monitors may read Gy in material; dose limits for workers are stated in Sv (often mSv).
• Research literature: Monte Carlo papers tabulate Gy; ICRP risk coefficients ingest Sv—confirm Q and tissue factors at the boundary.

Sievert to gray

Convert Sv to Gy when protection limits, effective dose cards, or incident briefings quote sieverts but Monte Carlo output, calibration phantoms, or treatment planning datasets list absorbed dose in gray.

When Q = 1 (photons and most electrons in soft tissue), equivalent dose in sieverts and absorbed dose in gray are numerically equal at the same point: 1 Sv ↔ 1 Gy. Divide or multiply by 1— the numeric value transfers, but the quantity name must still match the context.

D (Gy) = H (Sv) ÷ Q  ·  when Q = 1: Sv value = Gy value numerically

Step-by-step conversion (worked example)

An occupational log shows 0.008 Sv (8 mSv) whole-body photon effective dose:

1. For Q = 1 photon exposure: absorbed dose ≈ 0.008 Gy numerically
2. Display: 8 mGy only if the measurement truly reports absorbed dose—check the column header

Second worked example (when Q ≠ 1)

0.1 Sv equivalent from neutrons with Q = 10 implies:

1. D = H ÷ Q = 0.1 ÷ 10 = 0.01 Gy absorbed—not 0.1 Gy
2. Never assume 1:1 without identifying radiation quality

Quick reference (Sv → Gy when Q = 1)

Reverse conversion supports comparing ICRP Sv tables against Gy Monte Carlo tallies for photon/electron fields where Q is unity.

Absorbed vs equivalent dose, effective dose, mistakes, and related tools

Gray and sievert share catalog numeric anchors but differ in meaning. Q = 1 makes photon Gy and Sv numerically equal; mixed radiation fields need explicit weighting.

Gray vs sievert at a glance

Effective dose adds tissue weighting

Even when Q = 1, effective dose in sieverts applies organ/tissue weighting factors across the body. A CT report's mGy in one organ is not automatically the patient's mSv effective dose without ICRP coefficients. Gy→Sv unit algebra is only the first step.

Common mistakes to avoid

• Treating mGy as mSv with a prefix rule only — CTDIvol in mGy is not patient effective dose in mSv without conversion coefficients.
• Assuming 1 Gy always equals 1 Sv — true for Q = 1 fields; false for neutrons and alphas.
• Using Gy for occupational limits — worker caps are stated in Sv (mSv); absorbed dose in Gy may differ in mixed fields.
• Confusing Gy with rad — customary absorbed dose uses rad (1 Gy = 100 rad). See gray to rad.
• Ignoring partial-body vs whole-body geometry — 2 Gy tumor dose does not mean 2 Sv whole-body effective dose.

Exactness and catalog note

The catalog assigns Gray = 1 and Sievert = 1 on the same scale for converter arithmetic. Physical equivalence of numeric values requires Q = 1 (and appropriate geometry for effective dose). Converting 0.5 Gy → 0.5 Sv → 0.5 Gy round-trips numerically when Q = 1 throughout.

Related radiation converters

For the inverse orientation, open sievert to gray. Nearby workflows: sievert to millisievert, gray to rad, sievert to rem, and rad to gray.