For those needing portability, Rad Pro for Desktop works with Windows 8.1/10 tablets. Will not work with Surface tablets running Windows RT.
Ionizing Radiation Units
becquerels curies Activity Conversions

Select Conversion   Converted Units = Input Units Enter Value         
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Converts all common units of radioactivity measurement including activity units, dose equivalent units and absorbed dose units.  Also included are other common multi-unit calculations such as uCi/ml to pCi/L and dpm/100cm2 to Bq/cm2 (miscellaneous option button).  The calculator includes both SI and customary US radiation units.