Ygg, how does that help tho? How will you measure this mass in the context of the question?
Its kind of like saying that you will convert your home electricity usage into mass. Not very useful. That's not really what Einstein was meaning.
Some measurements make more sense than others. I can think of a couple ways to measure the energy as relates to this question. Measurement of mass wouldn't really make sense in this context.
Are you a physicist, or did you just grab that info from Google?
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh