X-ray equipment Constant potential 2-30 MV Fig 3.2 (6)

If you take the y-axis value and multiply by 600, this will give you a figure of mGy/ mA h at 1m. Note how exposure rate is significantly affected by filtration.

1 esu = 3.3 x 10^-10 coulombs = 2 x 10⁹ ion pairs/cm³ of air. Equivalent to 2.58 x 10^-4C/kg air (0.0087 J/kg of air). 1R is approximately 10 mGy (good enough for radiation protection purposes).