Why does background matter?

Background CPM should be subtracted from gross CPM to get net CPM. Net CPM is then corrected for efficiency to estimate net DPM.

What is detector efficiency?

Efficiency is the fraction of disintegrations your detector counts under your specific setup. It depends on detector type, isotope energy, geometry, settings, and counting time.

Is the formula (gross - background)/efficiency or gross - (background/efficiency)?

Use parentheses: net DPM = (gross CPM - background CPM) / (efficiency/100). The subtraction happens first.

Is this the marketing CPM (cost per mille)?

No. Here CPM means counts per minute (radiation counting), not cost per mille.

CPM to DPM conversion (radiation counting)

CPM to DPM Conversion Calculator

Convert gross CPM to net DPM using background subtraction and detector efficiency. Includes net CPM, a copyable summary, and optional AI insights.

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Calculator

This tool uses CPM = counts per minute and DPM = disintegrations per minute (radiation counting). It includes background subtraction to compute net CPM. It is not the marketing CPM (cost per mille) or textiles DPM (denier per meter).

Gross CPM (counts/min)

Background CPM (counts/min)

Detector efficiency (%)

Enter efficiency as a percentage (0–100). Use an efficiency measured for your isotope/setup.

Net CPM (gross - background)

120

Net DPM

600

AI insights

Get practical guidance based on your inputs and assumptions.

Avoid sharing personal or sensitive data. AI output is advisory and may be inaccurate.

Context (optional)

References

Authoritative explanations of CPM, DPM, efficiency, and background correction:

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Features

Two-way conversion

Convert gross CPM to net DPM or reverse: net DPM to gross CPM.

Net CPM included

Shows net CPM = gross CPM - background CPM before converting to DPM.

Copyable summary

Copy inputs, net CPM, result, formula, and assumptions for lab notes.

Optional AI insights

Get practical interpretation and pitfalls (with graceful fallback when AI is unavailable).

How it works

Collect inputs

Enter gross CPM (or net DPM), background CPM, and an efficiency measured for your setup.

Compute net CPM then net DPM

We subtract background first, then divide by (efficiency/100) to estimate net DPM.

Copy and document

Copy a clean summary and document assumptions and settings.

FAQ

Ready to convert CPM to DPM?

Compute net CPM and net DPM with background subtraction and efficiency.

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Disclaimer: This page is a calculator, not radiation safety guidance. Results depend on correct background and detector efficiency and your lab SOP.