What is the exact conversion between gray and rad?

1 gray (Gy) = 100 rad, exactly. Equivalently, 1 rad = 0.01 Gy. The relationship is fixed by definition and has no uncertainty.

Is gray the same as sievert?

No. Gray measures absorbed dose — physical energy deposited per unit mass. Sievert (Sv) measures effective dose, which weights the gray value by a radiation quality factor and tissue weighting factor to reflect biological harm. For X-rays and gamma rays, 1 Gy = 1 Sv numerically, but for alpha particles 1 Gy = 20 Sv.

When would I use rad instead of gray?

Rad is still widely used in the United States in radiology, radiation oncology, and regulatory documents. If you work with older US literature, legacy dose records, or certain federal regulations (10 CFR), you will encounter rad. International and modern scientific publications use gray.

What is a typical therapeutic radiation dose in gray?

A full course of radiation therapy for a solid tumor typically delivers 45–70 Gy, delivered in daily fractions of 1.8–2 Gy. In rad, that is 4,500–7,000 rad in 180–200 rad fractions.

Does this tool apply a radiation weighting factor?

No. Gray-to-rad is a direct unit conversion with no weighting. Both units measure absorbed dose without any biological correction. To convert to biological dose (sievert or rem), you would multiply by the appropriate radiation weighting factor (Q or wR).

Grays to Rad Converter

Convert absorbed radiation dose from grays (Gy) to rad; 1 Gy = 100 rad.

Input Dose

Absorbed Dose

Input Unit

Quick Reference

Gray (Gy)	Rad
0.001 Gy (1 mGy)	0.1 rad
0.01 Gy (10 mGy)	1 rad
1 Gy	100 rad
2 Gy	200 rad
50 Gy	5,000 rad

Result

rad

—

millirad (mrad)

—

microrad (µrad)

—

Formula

rad = Gy × 100

1 gray = 1 J/kg. 1 rad = 0.01 J/kg. The conversion factor is exact.

Copied!

Summary

The gray (Gy) is the SI unit for absorbed radiation dose, equal to one joule of energy deposited per kilogram of matter. The rad (radiation absorbed dose) is the older CGS unit still common in US medical and health-physics contexts; 1 Gy equals exactly 100 rad. This converter accepts any gray value — including mGy and µGy — and instantly returns the equivalent in rad, mrad, and µrad.

How it works

Enter the dose value in the input field.
Select the input unit: gray (Gy), milligray (mGy), or microgray (µGy).
The tool multiplies by the exact factor: 1 Gy = 100 rad.
Results display in rad, millirad (mrad), and microrad (µrad) simultaneously.
Use the Copy button to copy any result to your clipboard.

Use cases

Convert radiotherapy dose prescriptions from Gy to rad for legacy documentation.
Translate health-physics dose limits between SI and CGS unit systems.
Cross-check absorbed dose values in radiation safety reports.
Convert diagnostic imaging dose (CT, fluoroscopy) from mGy to mrad.
Study or teach the relationship between gray and rad in medical physics courses.
Verify dosimetry calculations when comparing US and international literature.

Frequently Asked Questions

Last updated: 2026-07-14 · Reviewed by Nham Vu