Things You'll Need
Set of king size sheets
8 inches of 1/4 inch elastic
Whether you are having trouble finding California King (Western) sheets or just can't afford them when you do find them, converting standard king size sheets could be the answer to your dilemma. It's a relatively easy process and the results look nice and do not compromise the comfort of the bedding.
Put the bottom of the fitted king size sheet on your bed and pull the top edge flat but do NOT put on. Draw a straight line across the bottom of the bed and down the sides. Cut along line.
Lay flat sheet out and draw a line 6 inches from outside edge the entire length; it doesn't matter which side. Cut along line. Hem side of sheet.
Sew a small hem on the left side of your long strip and run 4 inches of ¼-inch elastic through it. Sew the elastic closed on one end then gather the fabric across the elastic and sew the other end closed as well.
Align finished edge of strip with raw edge of the top of the fitted sheet. Sew a ½-3/4 inch seam down the entire length, stopping 2 inches before the right edge of the fitted sheet. The strip will be longer than the fitted sheet is.
Turn strip right side up and sew bottom of fitted sheet from finished edge of strip to within 2 inches of right edge.
Trim strip 1 inch longer than edge of fitted sheet and hem so it will meet the edges smoothly. Run 4 inches of ¼-inch elastic through the hem and secure on both ends. Sew remaining 2 inches on both sides. You can quit at this point and your fitted sheet will work fine. However, the following step takes you through making the fitted sheet narrower as well, which will tailor it to the California king mattress even more.
Put your fitted sheet on the bed and draw a line along the side of sheet and down the front and top; similar to what you did earlier for the bottom. Using a measuring tape measure 3 inches further toward the center of the sheet and make another line. Cut along both lines. Sew together with a ½ inch seam allowance.
If you prefer not to cut up your flat sheet you can use any light weight fabric or a spare flat sheet to accomplish the same thing. Check out more patterns and money saving ideas at http://www.makethemyourself.com.
Different manufactures make sheets differently so there may be some slight roominess with the length but not enough to make the sheet slip off.