Troughline Calculator

I've Googled in vain for an online calculator, or program for calculating
troughline dimensions - does anyone know of one, please?  The maths makes my
brain hurt!  

Something along the lines of  this coax line calculator is what I am looking
for:

 http://www1.sphere.ne.jp/i-lab/ilab/tool/cx_line_e.htm  

Thanks.