This is Part One of a two-part series on replacing sock heels. See our previous three-part sock-mending series covering how to do Swiss darning, stocking darning and Scottish darning.
One of the many benefits of knitting a toe-up sock, or any sock without a gusset, is that it’s very simple to replace the heel. The afterthought heel, forethought heel, short row heel and other related constructions may be used interchangeably for this style of sock and they all follow a similar replacement method. Toes are equally as simple to replace.

Simply put, all you need to do is to cut out the heel or toe, place the intact stitches on the needles, knit a new heel or toe, and graft the remaining stitches closed. Let me break it down for you.
Tools and Materials
Yarn: Choose a sock yarn that is the same weight as the original sock. Bonus points for finding a yarn with some nylon, silk, and/or mohair content and a tight twist. These properties lend their strength to the yarn; durability is the main goal with this type of repair.
Knitting needles: Circular or double pointed needles in a size that will result in the same gauge as the original sock. Optional, if you also have a smaller sized needle it will be easier to pick up your stitches.
Scissors: Sharp scissors to cut out the damaged heel.
Yarn needle (not pictured): Tapestry needle with a large eye for grafting.
Locking stitch markers (not pictured): Removable, safety-pin style markers.

All images by Holli Yeoh.