Instantly convert between CPM (counts per minute — the raw detector output) and µSv/h (microsieverts per hour — the dose-rate estimate). Select your Geiger tube type for the most accurate result.
Detector Tube
Conversion factors are tube-dependent. SBM-20 and M4011 are the most common in volunteer networks; J305 is popular in low-cost consumer devices. The same dose rate produces very different CPM values across tube types.
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Counts Per Minute
Microsieverts per hour
Typical CPM and estimated µSv/h values for common scenarios, using SBM-20 factor (×0.00833).
| Scenario | CPM | µSv/h | Level |
|---|---|---|---|
| Typical background (low altitude) | 20 | 0.17 | Safe |
| Typical background (high altitude) | 100 | 0.83 | Safe |
| Slightly elevated — worth watching | 600 | 5 | Monitor |
| Notably above normal | 1,500 | 12.5 | Caution |
| Significantly elevated | 3,000 | 25 | High |
| Serious — follow official guidance | 7,000 | 58.3 | Severe |
| Potentially life-threatening | 15,000 | 125 | Extreme |
CPM (Counts Per Minute) is the raw output of a Geiger-Müller tube — the number of ionising radiation events detected each minute. It is the most reliable way to compare readings within a single station over time, but CPM values are not directly comparable between stations with different tube types.
Microsieverts per hour (µSv/h) is a standardised dose-rate unit that accounts for how harmful different types of radiation are to human tissue. Typical background radiation is 0.05–0.20 µSv/h (roughly 6–24 µSv per day). The conversion from CPM to µSv/h depends on the specific detector tube; the values shown here use well-established factors for the most common consumer tubes.