For those needing portability, Rad Pro for Desktop works with Windows 8.1 tablets (just tested). 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.