Convert between sieverts, millisieverts, gray, rad, rem and more — instant results for absorbed and equivalent dose units.
Radiation dose is a measure of the energy deposited by ionising radiation in matter. Two closely related quantities are in everyday use: absorbed dose — measured in gray (Gy) or the older unit rad — describes the raw energy deposited per kilogram of tissue. Equivalent dose, measured in sievert (Sv) or the older unit rem, weights the absorbed dose by a radiation type factor (W_R) that reflects biological effectiveness. For the most common sources encountered clinically and environmentally — X-rays, gamma rays and electrons — W_R equals 1, so 1 Gy numerically equals 1 Sv.
This converter handles all common dose units in real time, grouped by quantity type: absorbed dose (Gy family and rad) and equivalent dose (Sv family and rem/mrem/BED). Type any value, choose the source unit, and every other unit updates instantly — no recalculation required.
All conversions use the sievert (Sv) as an internal base unit, assuming a radiation weighting factor W_R = 1. To convert from any unit to any other, multiply the source value by its sievert-equivalent factor, then divide by the target unit's factor:
Here f denotes the conversion factor (in sieverts) for each unit. For example, 1 mSv = 0.001 Sv, 1 rem = 0.01 Sv, and 1 Banana Equivalent Dose ≈ 0.1 µSv = 1 × 10⁻⁷ Sv.
Scale Factors
Absorbed ↔ Equivalent
Quick References
A standard chest X-ray performed in an NHS hospital delivers approximately 0.1 mSv — roughly the same as three days of natural background radiation in the UK. In millirem, that equals 10 mrem; in microsieverts, 100 µSv.
The average UK resident receives about 2.7 mSv per year from natural background sources — cosmic radiation, radon gas, food and building materials. Regions such as Cornwall, with high granite geology, can exceed 7 mSv per year due to elevated radon levels.
A diagnostic CT chest scan typically imparts 5–8 mSv of effective dose. At 7 mSv, the patient receives the equivalent of roughly 70,000 µSv, or 700 rem equivalent in the older unit system. Radiologists use dose-length product (DLP) to optimise protocols and minimise this exposure.
The UK Health Security Agency sets an annual occupational dose limit of 20 mSv for radiation workers averaged over five years, with no single year exceeding 50 mSv. In centigray (cGy), 20 mSv equals 2 cGy — the same number holds because W_R = 1 for the relevant radiation types.
Enter the dose value you wish to convert in the input field. Decimal values such as 0.05 and scientific notation are fully supported.
Select the source unit from the dropdown. All 11 units are listed with their full name and symbol for clarity.
The converter multiplies your value by the source unit's factor to obtain an intermediate value in sieverts (Sv), then divides by each target unit's factor.
Results are displayed in two groups: absorbed dose (gray family + rad) and equivalent dose (sievert family + rem/mrem/BED), so you can immediately identify the unit category.
Very large or very small results are shown in exponential notation (e.g. 1.23 × 10⁻⁷) to keep all values readable regardless of magnitude.
For X-rays and gamma rays (the most common medical and environmental sources), 1 Gy = 1 Sv because the radiation weighting factor W_R = 1. The converter applies this assumption throughout.
Radiotherapy doses are typically expressed in gray (Gy) or centigray (cGy). A 2 cGy fraction is a standard daily radiotherapy fraction and equals exactly 20 mGy.
Radiation protection and environmental monitoring commonly use millisieverts (mSv) or microsieverts (µSv). Annual natural background in most countries falls in the 1–10 mSv range.
The Banana Equivalent Dose (BED) is an informal unit — one banana ≈ 0.1 µSv — useful for communicating small doses to the public. It is not an official SI unit.
Rem and millirem are still widely used in the United States for regulatory reporting. 1 rem = 10 mSv and 1 mrem = 10 µSv.
The gray (Gy) measures absorbed dose — the physical energy (in joules) deposited per kilogram of any material. The sievert (Sv) measures equivalent dose — the absorbed dose multiplied by a radiation weighting factor W_R that accounts for the biological effectiveness of different radiation types. For X-rays, gamma rays and electrons W_R = 1, so the numerical values of Gy and Sv are identical. For neutrons or alpha particles W_R is greater than 1, meaning the equivalent dose in Sv is higher than the absorbed dose in Gy.
The radiation weighting factor W_R depends on the type of radiation (X-ray, gamma, neutron, alpha, etc.) and cannot be determined from a dose value alone. This converter applies W_R = 1, which is the correct value for gamma rays, X-rays and electrons — the radiation types encountered in the vast majority of medical, occupational and environmental contexts. A disclaimer is shown on the page to remind users of this assumption.
A routine chest X-ray delivers approximately 0.1 mSv (100 µSv) of effective dose. For comparison, the average annual natural background dose in the UK is about 2.7 mSv, so a chest X-ray represents roughly 13 days of natural background. A CT scan of the chest is considerably higher, typically in the range of 5–8 mSv.
Most regulatory frameworks worldwide set the occupational effective dose limit at 20 mSv per year averaged over a five-year period, with no single year exceeding 50 mSv. This is the limit recommended by the International Commission on Radiological Protection (ICRP Publication 103) and adopted by the EU, the UK and most other jurisdictions.
The Banana Equivalent Dose (BED) is an informal, educational unit equal to approximately 0.1 µSv (1 × 10⁻⁷ Sv). It represents the small additional dose from eating one banana, which contains a trace amount of naturally radioactive potassium-40. BED is used to put low-level doses into everyday perspective; it is not an official SI or ICRU unit and should not be used in formal dose calculations.
The rem (Roentgen Equivalent Man) and millirem (mrem) are older CGS units of equivalent dose, still commonly used in the United States. The conversion is straightforward: 1 rem = 0.01 Sv = 10 mSv, and 1 mrem = 0.001 rem = 10 µSv. Nuclear power plants, medical facilities and radiation laboratories in the US frequently report doses in mrem or rem for regulatory compliance.
This converter assumes a radiation weighting factor W_R = 1 (applicable to gamma rays, X-rays and electrons). For other radiation types (neutrons, protons, alpha particles, heavy ions), the sievert value will differ from the gray value. Always consult a qualified medical physicist or radiation protection adviser for clinical or occupational dose assessments.