Radioactivity calculator

Radioactively labeled compounds are commonly used in biological and chemical research. Use these calculators to perform the radioactivity calculations commonly used in setting up and analyzing biochemical and pharmacological experiments. Note that this page has seven independent calculators, and that the results will appear right on this page. How do these calculations work?

The calculators on this page are independent and can be used in any order. The calculators are numbered because sometimes the results of one calculator are used as inputs to a later one.

1. Isotope decay


Half life (days):

Number of days:

2. Concentration of stock

% remaining isotope:

Original dilution:

Original activity:

Assumes compound was 100% labeled originally (carrier free)

3. Dilution of stock

Concentration of stock solution (micromolar):

Dilute to this concentration in nM:

Final dilution volume in ml:

4. Specific activity (cpm/fmol)

Specific radioactivity:

Counter efficiency (%):

4.1. Cpm to fmol/mg



mg protein:

4.2. Cpm to sites/cell



cell count:

4.3. Cpm to nM




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