Custom lampshade makers typically require designers to provide substantially more fabric yardage than is actually necessary. This is result of the slightly involved arithmetic required to calculate how a 3-dimensional shape translates into 2-dimensional surfaces.
Using this calculator to generate a second opinion of (exact theoretical) yardage requirements, you can reduce waste and save money. (Make sure to increase this theoretical result to a practical yardage amount that contemplates hems, wire-wrapping, selvage, grain direction, pattern placement and bolt width!)
|b||Radius of inner cutout circle||6.5|
|c||Angle between radial cuts (angle of area discarded)||165|