When and why do you decrease stitches in knitting?

WHEN: When the hat is the correct length from the cast-on edge. Your instructions should tell you that. If you're not using instructions, you need to decide if you want a turned-up brim, a rolled-up brim, or a flat brim that doesn't turn up. For most babies' hats, you'd start shaping at between 5" and 6" from the cast-on edge or from the bottom of the brim, whichever applies.

WHY: If you started the hat from the brim up, you will likely be decreasing stitches to shape the crown of the hat so it's the same shape as the baby's head. That provides a snug fit.

Actually, there are three basic ways to finish the top of a hat:

1. Decrease stitches on alternate rounds until there are 10 or fewer stitches, then gather them onto the tail of the yarn and fasten off. Sew the back seam if there is one. To make a decorative "spiral" top, divide the number of stitches by 6 or 8 to make 6 or 8 segments. Knit the first segment until there are 2 stitches left; k2tog. Repeat on each segment around. Knit one round even, then repeat the decrease row. Repeat these two rows--decrease on one row, knit even on the next--until there one stitch left in each segment.

2. Don't decrease. Bind off the full number of cast-on stitches. Sew the back seam if there is one. Then match the center front to the center back and sew the top seam. Put pompoms or tassels on the two points at the corners. Or match the center front to the center back and pull the corners to meet the center front and center back for a hat top that has 4 points.

3. Don't decrease. Gather the full number of cast-on stitches on the tail of the yarn and pull it up to make a poofy top to the hat. Sew the back seam if there is one. Optionally put a big pompom on the top of the gather.

This link is to Bev's Country Cottage, which is Beverly Qualheim's repository of all sorts of hat patterns, all sorts of baby patterns, size charts, and other helpful information for knitting for babies and children. I hope it helps! http://www.bevscountrycottage.com/size-chart.html

Is there a link to the instructions you are using? That way it will be easier to see when the decreases occur. Basically, decreasing stitches is one of the ways to create some shape in the project you are knitting because you are subtracting stitches from your needle. The most common decrease involves inserting your needle through two stitches and knitting them together like you would with one stitch. The instructions may describe the decrease as "knit 2 tog". But check your instructions because there are different kinds of decreases. Every decrease subtracts one stitch from your stitch count. Your instructions should tell you where to perform the decreases so that they are evenly placed around the circumference of the hat. It sounds like you are knitting a hat that is wide at the brim and narrower at the top. You won't be able to achieve that shape without decreases.

You do each stitch the same as the previous row otherwise the border will not be rib.