Sievert to Rem Converter
Quickly convert from Sievert to Rem.
How to convert
Formula:
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Equivalent dose and effective dose account for the biological effectiveness of different types of ionising radiation.
Where is it used?
• Occupational Radiation Protection — Regulatory dose limits for radiation workers are set in millisieverts: 20 mSv/year averaged over 5 years (ICRP), 50 mSv in any single year, and 500 mSv to hands/feet as extremity...
Examples:
• 1 sievert (Sv) = 100 rem
• 1 rem = 10 millisieverts (mSv)
Equivalent dose and effective dose account for the biological effectiveness of different types of ionising radiation. The SI unit is the sievert (Sv), and the legacy unit is the rem (roentgen equivalent man). Because alpha particles cause ~20 times more biological damage per gray than X-rays, equivalent dose multiplies absorbed dose by a radiation weighting factor. Effective dose further accounts for the varying sensitivity of different body organs, enabling comparison of risks from different exposure scenarios.
Equivalent dose H = D × wR, where D is absorbed dose in gray and wR is the radiation weighting factor (1 for X/gamma, 2 for protons, 5–20 for neutrons depending on energy, 20 for alpha particles). Effective dose E = Σ wT × HT sums over all tissues T, each weighted by its tissue weighting factor wT (e.g., 0.12 for colon, 0.08 for lung, 0.04 for thyroid). Effective dose enables comparison of stochastic cancer risk from partial-body or whole-body exposures. Units: sievert (Sv) for both; rem in legacy US practice (1 Sv = 100 rem).
Where is it used?
- Occupational Radiation Protection — Regulatory dose limits for radiation workers are set in millisieverts: 20 mSv/year averaged over 5 years (ICRP), 50 mSv in any single year, and 500 mSv to hands/feet as extremity limits.
- Medical Imaging Risk Communication — Radiologists and radiographers communicate patient radiation risks using effective dose in mSv; a chest X-ray ≈ 0.02 mSv, a CT of the abdomen ≈ 8 mSv, allowing comparison with natural background (~2.4 mSv/year globally).
- Nuclear Accident Dose Assessment — Post-accident assessments (Chernobyl, Fukushima) report committed effective dose to populations in millisieverts, informing evacuation decisions and long-term health monitoring.
- Aviation & Space Dosimetry — Aircrew and astronauts accumulate higher cosmic radiation doses; a transatlantic flight adds ~0.05–0.1 mSv; ISS astronauts receive ~1 mSv/day, monitored in microsieverts per hour.
Common Conversion Mistakes
Treating sievert and gray as identical for all radiation types
For X-rays and gamma rays the radiation weighting factor wR = 1, so 1 Gy = 1 Sv numerically. But for alpha particles wR = 20, so 1 Gy of alpha radiation = 20 Sv. Assuming 1 Gy always equals 1 Sv underestimates the biological hazard of neutron, proton, or alpha radiation by factors of 2 to 20.
Confusing equivalent dose (organ) with effective dose (whole body)
Equivalent dose H applies to a specific organ or tissue. Effective dose E = Σ wT × HT is a weighted sum across all organs and represents the risk-equivalent uniform whole-body dose. Regulatory limits on 'dose to the lens of the eye' (150 mSv/year) are equivalent dose limits; the 20 mSv/year occupational limit is an effective dose limit. Using the wrong quantity leads to incorrect compliance assessment.
Misinterpreting microsievert values from consumer devices
Consumer radiation monitors often display μSv/h (ambient dose rate in microsieverts per hour). To get annual dose you must multiply by 8,760 hours — but only if the exposure is continuous. Background rates of 0.1–0.3 μSv/h correspond to 876–2,628 μSv/year (0.9–2.6 mSv/year), within the global average. Alarmist interpretation of momentarily elevated readings ignores the need to integrate over time.
Quick Reference Table
| From | To |
|---|---|
| 1 sievert (Sv) | 100 rem |
| 1 rem | 10 millisieverts (mSv) |
| 1 millisievert (mSv) | 1,000 microsieverts (μSv) |
| Global average background dose | ~2.4 mSv/year |
| Chest X-ray effective dose | ~0.02 mSv |
| Abdominal CT effective dose | ~8 mSv |
| ICRP occupational limit | 20 mSv/year (5-year average) |
Frequently Asked Questions
What is the difference between effective dose and equivalent dose?
Equivalent dose H (Sv) = absorbed dose D (Gy) × radiation weighting factor wR for a specific tissue or organ. Effective dose E (Sv) = the weighted sum of equivalent doses across all organs, using tissue weighting factors wT that reflect each organ's cancer and hereditary risk sensitivity. Effective dose is the quantity used for regulatory limits and risk communication; equivalent dose appears in limits for specific organs such as the lens of the eye or the skin.
How does the sievert compare to the rem?
1 sievert = 100 rem. The rem was defined in the CGS system as the dose in rad multiplied by a quality factor Q (conceptually equivalent to wR). The sievert replaced the rem in SI: 1 Sv = 1 J/kg × wR. In practice: 1 mSv = 0.1 rem; 20 mSv (ICRP annual worker limit) = 2 rem; background dose ~2.4 mSv/year = 0.24 rem/year. The rem is still found in NRC regulations and US nuclear power plant documentation.
How much radiation exposure is actually harmful?
The linear no-threshold (LNT) model — the basis of current regulation — assumes any dose carries some risk. However, epidemiological evidence shows no statistically detectable harm below ~100 mSv acute whole-body dose. Regulatory limits (20 mSv/year for workers, 1 mSv/year for the public) include large safety margins. Annual background exposure (~2.4 mSv) is not associated with measurable harm. Acute doses above 1,000 mSv (1 Sv) cause acute radiation syndrome; above ~6,000 mSv (6 Sv) are lethal without treatment.
What does a microsievert mean in everyday terms?
1 microsievert (μSv) = 0.001 mSv — a tiny dose. Relatable examples: eating one banana ≈ 0.1 μSv (potassium-40); a dental X-ray ≈ 5 μSv; one hour at typical cruising altitude ≈ 3–6 μSv; a mammogram ≈ 400 μSv; an abdominal CT ≈ 8,000 μSv (8 mSv). Annual background radiation globally averages 2,400 μSv (2.4 mSv). These comparisons help contextualise radiation dose without causing unnecessary alarm.
Sources & Standards
- ICRP Publication 103 — The 2007 Recommendations of the International Commission on Radiological Protection
- UNSCEAR 2008 Report — Sources and Effects of Ionizing Radiation
- NCRP Report 160 — Ionizing Radiation Exposure of the Population of the United States
- IAEA Safety Standards Series GSR Part 3 — Radiation Protection and Safety of Radiation Sources
Reviewed by The Unit Hub Editorial Team · March 2026