Radiation Absorbed Dose converter

The gray is the SI unit of absorbed dose — the amount of radiation energy deposited per kilogram of matter — and a joule per kilogram is that same definition written out in base SI units rather than as a named unit. The rad is the older unit still common in US medical and regulatory paperwork, and the relationship is clean: one gray equals exactly 100 rad, with the CGS erg per gram sitting underneath rad the same way joule per kilogram sits underneath gray. Because joule per kilogram is just the gray spelled out in base units, any formula that computes dose from energy deposited and mass absorbing it will always land in gray without needing a separate conversion step.

The milligray-to-millirad rule is mrad = mGy × 100, and the reverse direction multiplies by 0.01.

A diagnostic CT scan depositing roughly 15 mGy in the scanned tissue converts to 1.5 rad. A smaller reading of 5 mGy converts to 500 mrad — numbers that look very different in size even though they describe the same physical dose. Working the arithmetic the other way, 1.5 rad converts back to exactly 15 mGy, confirming the hundredfold relationship holds cleanly in both directions.

Absorbed dose in gray or rad is what radiation oncologists work with when planning a treatment course, what medical physicists use to characterize CT, X-ray, and nuclear medicine procedures, and what industrial radiographers and nuclear plant health physicists track when documenting exposure to equipment and materials — it is a physical energy measurement, independent of what absorbed it. Radiation safety training materials often walk through both units side by side specifically because a technician moving between a US facility and an international one may encounter either convention in daily paperwork.

The dose that matters for biological risk is not absorbed dose alone but absorbed dose adjusted for how damaging a given radiation type is, which is a separate quantity measured in sievert or rem, not gray or rad. Two exposures both reported as "1 Gy" can carry very different biological risk if one is from X-rays and the other from alpha particles, so gray and rad describe energy deposited, not harm done.

Because kilogray, gray, milligray, and microgray span nine orders of magnitude, it's worth double-checking which prefix a reported figure actually uses before converting by hand — industrial sterilization doses are routinely quoted in kilogray, while diagnostic imaging doses are almost always in milligray or microgray, and mixing up a single prefix changes the answer by a factor of a thousand. A quick way to catch such an error is to check whether the result is a plausible real-world dose — diagnostic doses are almost always well under 100 mGy, so a result in the thousands should prompt a second look at which prefix was actually used.

Because the gray is defined as one joule of absorbed energy per kilogram, dose figures in gray translate directly into an energy budget: a 2 Gy radiotherapy fraction deposits 2 joules in every kilogram of tissue it passes through, which helps explain why such a seemingly small energy figure can still cause significant biological effect at the cellular level. Food irradiation and medical-equipment sterilization, by contrast, operate in the kilogray range, doses thousands of times larger than any therapeutic or diagnostic figure, which is why kilogray and microgray sit at opposite ends of the same table.