Medical Radiation Dose Calculator (X-ray & CT effective dose in mSv)

Understanding the medical radiation dose calculator — concept and principle

This calculator adds up the typical effective dose, in millisieverts (mSv), from X-rays, CT scans and other imaging you have had, and compares the total with natural background radiation and with chest X-rays. It helps patients put imaging doses in perspective.

Doses add up: with the default inputs the result is 2.11 mSv (≈ 257 days of background).

How it is calculated

Total dose (mSv) = Σ (number of exams × typical dose per exam)

Same as natural background for (years) = total ÷ background rate; days = years × 365.25

Equivalent chest X-rays = total ÷ 0.1

Typical adult doses: chest X-ray 0.1, dental X-ray 0.005, mammogram 0.4, spine X-ray 1.5, extremity X-ray 0.001, CT head 2, CT chest 7, low-dose lung screening CT 1.5, CT abdomen and pelvis 10, coronary CT angiography 12, PET/CT 25, upper GI barium study 6 mSv.

The principle

Effective dose weights the radiation absorbed by each organ by that organ's sensitivity, so exams of different body parts can be compared on one scale related to long-term cancer risk. Everyone also receives natural radiation from radon, cosmic rays, soil and food, about 3 mSv a year in the US and Korea and 2.4 mSv as a world average. Expressing a medical dose as days of background makes it easier to understand.

Worked example

Default inputs: 1 chest X-ray, 2 dental X-rays, 1 CT head, background 3 mSv/year.

Total = 0.1 + 2 × 0.005 + 2 = 2.11 mSv.
Background equivalent = 2.11 ÷ 3 = 0.7 years = 0.703 × 365.25 = 257 days.
Chest X-ray equivalents = 2.11 ÷ 0.1 = 21.
Share from CT = 2 ÷ 2.11 = 95%.

Each point is the calculator re-run with only “CT head (2 mSv each)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

CT head (2 mSv each)	Total effective dose (mSv)
0.25	0.61
0.5	1.11
0.75	1.61
1	2.11
1.25	2.61
1.5	3.11
2	4.11

How to read the result

Most imaging doses are small compared with a lifetime of background radiation, and a needed test usually benefits you far more than its small risk. CT and nuclear medicine contribute most of the dose. Real doses vary several-fold with the machine, protocol and body size, so the result is a rough guide.

Common mistakes

Counting ultrasound or MRI, which use no ionising radiation.
Treating typical values as your exact dose.
Avoiding a necessary scan because of a small estimated dose.

Keep in mind: This is an educational estimate, not medical advice. Discuss imaging decisions with your doctor; pregnant patients should always tell staff before an exam.

Frequently asked questions

Is a CT scan dangerous?

The dose is higher than an X-ray, and the very small added risk is usually outweighed by the benefit of a needed scan.

How much radiation is in a chest X-ray?

About 0.1 mSv, roughly 12 days of natural background at 3 mSv a year.

Can I find my actual dose?

Some CT reports show dose values; your radiology department can explain them.

Sources: ACR and RSNA, RadiologyInfo.org, "Radiation Dose to Adults From Common Imaging Examinations" · Mettler FA Jr et al., "Effective doses in radiology and diagnostic nuclear medicine: a catalog", Radiology 2008;248(1):254–263 · UNSCEAR 2008 Report, Sources and Effects of Ionizing Radiation

Checked 9 Nov 2026. American College of Radiology & Radiological Society of North America, RadiologyInfo.org “Radiation Dose to Adults From Common Imaging Examinations” (dose reference card, edition 05.18); catalogue values in Mettler FA et al., “Effective doses in radiology and diagnostic nuclear medicine: a catalog”, Radiology 2008;248(1):254–263; background: NCRP Report No. 160 (2009, US ≈ 3.1 mSv natural) and UNSCEAR 2008 (world average 2.4 mSv).

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