I'm making pillowcases for Christmas for the travel pillows my daughters and nieces have (Don't worry, they all get plenty of 'real' gifts and even some of those from me) and I thought I'd give a simple tutorial. I've given measurements before, but these are a really simple way of making a high quality pillowcase. After Christmas, I plan on making myself some body pillow cases since my body pillow that is actually supportive and good for my back doesn't actually fit in pillow cases that you can buy for body pillows (though they fit the cheapo $10 body pillows fine).
First, cut and iron your main fabric.
Travel case: 18 inches x 28 inches.
Standard case: 27 inches x 45 inches (or as close as you can get it width-wise).
Body pillow case: 50 inches x 45 inches (I wouldn't choose a fabric that is much less than 44 inch in width).
If adding trim, cut and iron the trim
Travel case: 3 inches x 28 inches.
Standard case: 3 inches x 45 inches.
Body pillow case: 3 inches by 45 inches.
Cut and iron the flange.
Travel case: 7 inches x 28 inches.
Standard case: 12 inches x 45 inches.
Body pillow case: 20 inches by 45 inches.
Next, fold the trim piece in half with wrong sides together and iron.
Place the flange fabric face up. Place the main fabric face up on top of it lining up the edge. Place the folded trim piece face up on that and again line up the edge.
Roll up the main fabric to where there is plenty of room to fold the flange in two.
Fold the flange over and line up all the edges.
Sew across the top (I use 1/4 inch seam here).
Pull all the fabric out of the tube.
Unroll the tube.
Now for the French seams. This gives both sides a nicer and stronger finish. Fold the fabric in two with wrong sides together.
Sew around using a seam 1/8-1/4 inch smaller than your usual seam. (If you are a precision sewing, use 1/8 inch seam like I do. A beginner should use 1/4 inch seam.) On this pillow I actually turned my trim up which is why the flange looks smaller than the previous pictures. Trim the seam to 1/8 of an inch or if it is frayed.
Turn inside out and press.
Sew again. (I use 1/4 inch seam here. Beginners should probably use 1/2 inch).
Turn back right side out and press. In the even that there are threads or part of the earlier seam sticking out, you can simply turn back inside out and sew the seam a little further out at that point.
Here is a view of the final pillow case on the pillow.
Edited 12/19 to add trimming suggestions for stray threads or showing seams.