A quick script to give real filament diameter from a measured 1 shell printed wall.

filament_size.py

import argparse
import math

argp = argparse.ArgumentParser()
argp.add_argument("measured", type=float, help="Measured wall width")
argp.add_argument("nozzle", type=float, default=0.4, nargs="?", help="Nozzle width (or what the wall is supposed to measure) default=0.4")
argp.add_argument("filament", type=float, default=1.75, nargs="?", help="Filament diameter, default=1.75")
argp.add_argument("-n", "--nozzle", type=float)
argp.add_argument("-f", "--filament", type=float)

args = argp.parse_args()

volume_overextrude = args.measured / args.nozzle
print  volume_overextrude

# pi*r_for_measured^2 / pi*r_for_filament^2 = volume_overextrude
# r_for_measured^2 / r_for_filament^2 = volume_overextrude
# volume_overextrude * r_for_filament^2 = r_for_measured^2
# r_for_measured = sqrt(volume_overextrude * r_for_filament^2)

new_r = math.sqrt(volume_overextrude * (args.filament/2)**2)
new_d = new_r * 2

print "Adjusted filament diameter = %s" % new_d