Wire length is calculated by (diameter x π x turns). π
is taken to be 3.14159265358979323846264338327950288419716939937510
which is a little over the top I know! As 39 decimal places is sufficient to
estimate the
circumference of any circle that fits in the observable universe with
precision comparable to the radius of a hydrogen atom, the 50 decimal
places I have used should be OK for your inductor. Just remember to cut
a bit longer
for some tails! 
