Question: 1 roentgen equals how many rem?
Answer: Considering FAQ 1 above, we know that 1 rad equals 1 rem and 1 Gray equals 1 Sievert, for gamma rays. Since 1 Roentgen equals 0.877 rad, then 1 Roentgen equals 0.877 rem and 1 Roentgen = . 00877 Sieverts.