What is the exact relationship between rem and sievert?

1 rem = 0.01 Sv exactly. Equivalently, 1 Sv = 100 rem. The millirem (mrem) is therefore equal to 0.00001 Sv (10 µSv). This factor is defined, not measured, so there is no rounding involved in the conversion itself.

Why is the rem still in use if the sievert is the SI unit?

The US Nuclear Regulatory Commission (NRC) and the US Department of Energy (DOE) historically used the rem in regulations and dose limits. Changing all regulatory text and dose-monitoring records is a slow process. Many US workplaces, hospitals, and dosimetry reports still express dose in rem or mrem, while international bodies (ICRP, IAEA, WHO) use sieverts.

What is a typical background radiation dose in rem and sievert?

Average annual background radiation in the United States is approximately 0.31 rem (3.1 mSv) from natural sources plus roughly 0.31 rem (3.1 mSv) from medical imaging, for a total of about 0.62 rem (6.2 mSv) per year per person (NCRP Report 160, 2009).

What is the US annual occupational dose limit in both units?

The NRC limit for radiation workers is 5 rem per year whole-body effective dose, which equals 50 mSv per year — the same limit recommended by the ICRP (Publication 103, 2007) for planned occupational exposure.

Is rem the same as rad?

No. The rad (radiation absorbed dose) measures absorbed energy per unit mass (1 rad = 0.01 Gy), while the rem accounts for the biological effectiveness of different radiation types by multiplying the rad value by a quality factor Q. For X-rays, gamma rays, and beta particles Q = 1, so 1 rad = 1 rem for those types. For alpha particles Q = 20, so 1 rad of alpha equals 20 rem.

Can I use this for regulatory dose assessment?

This tool is for educational and quick reference use. Regulatory, occupational, and clinical dose assessments must be performed using authoritative dosimetry methods and reviewed by a qualified health physicist or radiation safety officer.

Rem to Sieverts Converter

Enter a dose value in rem and get the equivalent in sieverts, millisieverts, microsieverts, and millirem instantly.

Input

1 rem = 0.01 Sv (exact)

Dose value

Quick examples

Results

Enter a value and press Convert

Common dose reference values

Source / context	rem	mSv
Average US annual background (natural + medical)	0.62	6.2
Chest X-ray (single film)	0.001	0.01
Abdominal CT scan	0.1	1
US NRC annual occupational limit	5	50
Acute dose threshold for radiation sickness	≥ 75	≥ 750

Sources: NCRP Report 160 (2009); US NRC 10 CFR Part 20; IAEA Safety Reports. Values are approximate and represent typical adult whole-body effective dose.

Summary

The rem (roentgen equivalent man) is a non-SI unit of radiation equivalent dose still widely used in US regulatory and occupational health contexts. The sievert (Sv) is the SI unit for the same quantity. The conversion is exact: 1 rem = 0.01 Sv, or equivalently 100 rem = 1 Sv. This tool converts any rem value — including millirem (mrem) and the full rem range — to sieverts, millisieverts (mSv), and microsieverts (µSv), making it straightforward to translate US occupational exposure limits and medical dose records into SI units.

How it works

Enter the dose value in the input field and choose the input unit (rem or millirem).
The conversion applies the exact factor: 1 rem = 0.01 Sv.
Results are shown in sieverts (Sv), millisieverts (mSv), microsieverts (µSv), and millirem (mrem).
Use the quick-example buttons to load common reference doses.
Click "Copy result" to copy the primary sievert value to your clipboard.

Use cases

Translating US NRC annual occupational exposure limits (5 rem/year) into SI units (50 mSv/year).
Converting medical imaging dose reports written in rem or mrem to mSv for international comparison.
Health physics coursework requiring SI-unit homework answers from rem-based textbook problems.
Cross-checking radiation survey meter readings when the instrument displays rem and the report needs mSv.
Converting historical nuclear industry dose records from rem to sieverts for modern databases.
Quick sanity-checks when switching between US regulatory documents and ICRP or IAEA publications.

Frequently Asked Questions

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