Original poster: "colin.heath4 by way of Terry Fritz <twftesla-at-qwest-dot-net>" <colin.heath4-at-ntlworld-dot-com> hi all my ee is rusty and im trying to build homemade caps what is the formula is it Eo x Er x A ------------- d where EO = 8.85E-12 Er of polyethylene 3 A area of plate d distance between plates cheers colin heath