It appears that the dimensions in Inkscape are in "thousands" (.001) of an inch, and that the radius in Ink is 27.5 (0.0257"), The circle diameter is 27.5 x 2 / 1000 (0.055"). The stroke-width in Ink is 20 (0.020"), 20 / 1000. Half of the stroke-width is inside the circle and half outside the circle, but there are two sides (0.020" \ 2 * 2 = 0.020")... that's right, still 0.020". Take the diameter of the circle, minus the stroke-width = drill hold size (0.055" - 0.020" = 0.035"). In other words (27.5 * 2) - 20 = 35 (0.035").
In the Gerber drill file it my read something like "T100C0.034993", but it will be rounded up to the next drill size at the fab house. (Tool 100 = 0.035") plated hole size. The actual drill bit size may be a few 10/1000" larger to account for the finished platted hole size to 0.035" (0.889 mm).