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What Is CPM in Radiation?

What Are Counts Per Minute in Radioactivity?

When you get a Geiger counter and are learning how to use it, you’ll need to know about CPM, which is the counts per minute that you’ll see displayed on the analog meter in addition to the corresponding level of radiation. You might sometimes see counts per second, or CPS, instead, or you can easily convert from CPM to CPS if you’d like by dividing your CPM value by 60. So what is the CPM reading all about?


View Radiation Detectors that Measure CPM

How Does CPM Work?

The counts per minute measurements are generally used to pick up the number of particles around, which could include alpha or beta particles. A different level of measurement tends to be used for rays, including gamma rays and X-rays.

Instead of showing how much radiation something is giving off, the CPM radiation levels tell how many detection events the meter picks up. So the CPM amount doesn’t show you the amount or strength of the radiation. The device that you’re using to measure radiation can then also tell you the dose rate, although the conversion from CPM to dose rate will vary based on your specific device and some other factors, such as the kind of radiation. A Geiger meter uses energy compensation to create a reading of the dose.

While the measuring rate is “counts per minute,” the device often takes a sample from less time than the full minute and then determines what the total would be for the minute based on that sample.

What Does the CPM Value Mean?

Once you get your CPM reading from your device, you then need to figure out what that reading means. What are normal radiation levels CPM and what are dangerous ones? If you have your Geiger counter calibrated to Cs137, which most are, 1 milliRad per hour would equate to 1,200 CPM on your counter. At the same time, 1 microSievert per hour would equate to 120 CPM on the reading. These are more universal units of measurement that can help you better understand your radiation exposure.

A CPM reading of at least 100 is considered a warning level by the Radiation Network, although the length of time you’re exposed to the radiation is an important factor. If you’re concerned about staying within safe radiation levels, Ken Jorgustin explains on the Modern Survival Blog that it would take 432 days at a CPM of 100 to up your chance of getting cancer to odds of 1 in 1,000. At higher exposure rates, it would take less time. For instance, it would only take four days to increase your rate to those odds if you’re exposed to a level of 10,000 CPM.

When you use a Geiger Mueller detector, you’ll be able to easily see the counts per minute of radiation in a certain area. This can help you understand more about your environment and your exposure.

Browse Radiation Detectors that Measure in CPM


Nov 19, 2020 • Posted by Anthony W Mitchell

I’m getting readings as high as 1,609 CPM in my living quarters. I got nothing until the beginning of July 2020. Now my Geiger counter is going off much more frequently… Sometimes for an hour or two at levels over 100 CPM. The levels are peeking higher too. Most of the time it’s not going off??? I’m not sure what to make of it. It’s really getting annoying and I’m starting to worry. Am I safe or what?

Nov 19, 2020 • Posted by Alexander sesslar

4000 cpm?

Jun 29, 2020 • Posted by Yu Minhua

What about 2200 a guy on YouTube had pre war utensils and they read that

Mar 04, 2020 • Posted by Saas

@Jwfro wtf man, 1200 cpm, where do you live???

Mar 04, 2020 • Posted by Can you tell me the acceptable CPM levels on scrap metal at the scrap yards?

What’s the acceptable CPM level for metal being sold at a scrap yard?

Mar 04, 2020 • Posted by Kenneth W Robinson

1200 cpm in your living quarters is hot as hell and get out of there and away immediately … do not believe anyone who says this is ok … ie; doctors, any nuclear science expert, MIT or DOE…
All man made radiation is deadly to humans and anyone who says different is a liar and criminal ..,
Please educate yourself and see who is telling the truth…
Your Geiger counter when calibrated correctly will only acknowledge man made radiation on it and not natural background radiation which is harmless to us.

Mar 04, 2020 • Posted by someguy398

“I’m reading 1200 + cpm in my living quarters is this cause for concern its over everything”

Probably radon. Get tested for radon.

Mar 04, 2020 • Posted by Uhoh

Got some marbles doped in radium and they are >600 cpm, is this cause for concern?

Apr 03, 2018 • Posted by Artyom

@Jwfro Where do you live, Chernobyl?

Feb 27, 2018 • Posted by Jwfro

I’m reading 1200 + cpm in my living quarters is this cause for concern its over everything

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