Radiation Dose Converter

Converts radiation dose values between sieverts (Sv), millisieverts (mSv), microsieverts (µSv), and the older rem and millirem units. The base relationship is 1 Sv = 100 rem.

Sievert is the SI unit of equivalent dose, weighted for biological effect. Rem is its CGS-era counterpart, still used in US regulatory and medical contexts. Conversion is exact and linear; no biological context is inferred.

The unit lineage matters for reading regulatory and medical documents correctly. The roentgen (R) measures exposure (ions per kilogram of air). The rad (radiation absorbed dose) measures energy deposition per kilogram of tissue. The rem (roentgen equivalent man) weights rad by a quality factor reflecting the biological effect of different radiation types: 1 for X-rays and gamma rays, 10 for fast neutrons, 20 for alpha particles. The sievert applies the same weighting in SI base units. For X-ray and gamma exposure, the rad-to-rem and gray-to-sievert conversions are unity; for alpha and neutron exposure, they diverge significantly.

A worked example: a chest CT scan delivers approximately 7 mSv of equivalent dose. Converted to legacy units: 700 mrem, or 0.7 rem. Annual background radiation in Denver (5,280 ft elevation) is roughly 4.5 mSv versus 3 mSv at sea level — the difference comes from cosmic ray attenuation through the atmosphere. A flight from New York to Tokyo delivers about 0.1 mSv. Living within 50 miles of a coal plant for a year delivers about 0.0003 mSv; the same period near a nuclear plant delivers about 0.0001 mSv. The fly-ash from coal contains trace uranium and thorium.

The threshold for acute radiation syndrome is roughly 1 Sv (100 rem) delivered in hours. Lethal dose at 30 days without treatment (LD50/30) is roughly 4.5 Sv (450 rem). Long-term cancer risk from chronic low-dose exposure follows the linear no-threshold model in regulatory practice, though the empirical evidence below 100 mSv is weak. The 1-in-1,000 cancer risk per 100 mSv lifetime exposure is a regulatory convenience as much as a measured fact.

Limitations: the converter handles equivalent dose only. Effective dose (which weights different organ sensitivities) shares units but not values. A 1 mSv chest X-ray and a 1 mSv whole-body exposure carry different cancer risks. Confusion between equivalent and effective dose is common in casual reporting. Medical and regulatory contexts specify which is intended.