This is dead easy if your pillow has a cover.
- take cover off, measure across and down
- add one inch to each of these measurements
Uncovered pillow or pillow form:
- use your measuring tape to conform to the curve of the pillow and take the measurements from seam to seam
- add one inch to each of these measurements!
In this instructable, I'm covering a 16x26 inch pillow, so I'd consider my measurements to be 17x27.
We'll be cutting out three pieces all together, one for the front and two for the back. Many other tutorials just have you cut one long piece, but the I believe the extra seams make for a better fitting pillow. :)