How to Make Fitted Sheets
I have sewn many crib sheets, starting with sheets for my own son's crib when he was quite small (over 20 years ago). This is a great project for baby shower gifts.
This project can be completed with the help of a rotary cutter, which is not required if you can cut relatively straight lines.
Three yards of flannel yields a fitted crib sheet and a fair-sized flat sheet. The fabric remaining after making the fitted sheet can be turned into a flat sheet by rounding the corners and finishing the edges (instructions below).
Larger beds require wider fabric. Some fabrics are available at 90" and some at 120". These fabrics are usually all or mostly cotton. Look for quilt backing at Hancock's and Joann's, both in the stores and online.
Wash and dry the fabric at least three times before using. This will help keep future shrinkage under control.
Modern crib sheets are approximately 52.25" X 28" X 6". I do not have the measurements for any other size, because all other mattresses vary so much in size. You will need to measure the mattress before you start this project.
Here are the formulas you need:
Lm = Length of mattress
Wm = Width of mattress
Hm = Height of mattress
Ws (Width of sheet) = Wm + ( 3 x Hm) + 0.5"
Ls (Length of sheet) = Lm + (3 x Hm) + 0.5"
Sq = Hm x 1.5
Buy fabric at least at wide as Ws as calculated above (must be at least as wide as 2xHm + Wm + 2) and at least as long as Ls. Also have lots of braided or knit elastic that is 1/4" or 3/8" wide. Machine wash and dry the fabric at least two times, but not the elastic.
Cut the fabric to size where width = Ws and length = Ls. If the fabric is not quite wide enough, cut the fabric to length = Ls.
Fold the fabric in half width wise (matching cut ends) and also lengthwise (matching selvedges).
If you are able to cut to the exact size, cut a square out of each unfolded corner where the sides of the square are all = Sq. The picture shows both folds along the bottom, with the cuts taken from the far corner.
If you are unable to cut to the exact size, measure the short edges from the fold for length = (Wm / 2) + 1/4", and the long edges from the fold for length = (Lm / 2) + 1/4". The cuts will be on the corner that has no fold.
At each corner of the sheet, serge both arms of the corner (where the square was cut out) right sides together in a 1/4" seam, starting at the fold. The picture shows a corner ready to be sewn.
If a serger is not available, sew a 1/4" seam with a straight stitch followed by zigzag over the edges of the seam, or use a stitch which is a combination of both.
If the edges of this miter are not the same length, stitch approximately Hm distance from the corner, pull the shorter edge of the fabric to the right while sewing the underlap. This forces the long edge to follow an imaginary curve on the shorter edge's corner.
This example shows the shorter piece on top:
This example shows the longer piece on top:
Serge or zigzag all unfinished edges of the sheet. Hide all thread tails.
When I apply elastic to a crib sheet, I start at the side, 11" from the corner. For the king-size sheet, start about 20" from the corner.
On the long sides of the sheet, mark the distance from each corner. Permanent markers work great because the marks will be hidden under the mattress.
With the cut end of the elastic at the mark, lay the elastic on top of the wrong side of the sheet, with elastic and fabric edges together. Firmly tack the end of the elastic to the edge of the sheet. Stretch the elastic as much as possible for the entire distance. Switch to a multi-step zigzag stitch ...
... then stitch through the elastic towards the nearest corner, across the end of the sheet, and on the other side of the sheet to the other mark. Firmly tack the elastic to the fabric at the second mark, then cut off the loose remainder of the elastic.
Repeat this process at the other end of the sheet.
If you have extra fabric after making the crib sheet, here's how to make the matching flat sheet:
True up the remaining rectangle of fabric. If you don't have a serger, make a narrow hem on all edges.
If you have a serger, fold the fabric in quarters, matching up the corners. Place a small saucer over the fabric in the only place where four corners meet without any folds, and cut around the saucer. Open up the fabric and serge all around.