How do I cast on and cast off knitting neatly?

The long-tail cast on, judging how much tail to leave, and why a tight cast-off edge ruins an otherwise good piece.

Difficulty: beginner
Time: 20 min
Read: 3 min

Short answer

For the cast on, leave a tail of roughly three times the width of your finished piece, and use a long-tail cast on for a neat elastic edge. For the cast off, work it a needle size larger or deliberately loosely — a tight edge is the single most common finishing fault.

Both edges of a knitted piece are made differently from the rest of it, and both have almost no stretch unless you deliberately make them stretchy. That matters enormously on anything that has to go over a head or a foot.

Step by step

Estimate the tail before casting on.About three times the width of the finished piece, or roughly 2.5cm of tail per stitch on double knitting. Running out of tail halfway through means starting again.
Use a long-tail cast on as the default.It produces a neat, slightly elastic edge that suits almost everything and it is quick once learned. It counts as the first row, which trips people up when following a pattern.
Keep the cast-on loops loose enough to move.Each loop should slide freely on the needle. A tight cast on gives an edge that will not stretch, and it makes the first row extremely difficult to work.
Count as you go.Place a marker every twenty stitches on a long cast on. Recounting a hundred and twenty stitches three times is how an evening disappears.
Use a cable cast on for a firm edge.Where you want a defined, less stretchy edge, such as a buttonband. Worth knowing as a second method.
Cast off in pattern.Knit the knits and purl the purls as you cast off. It keeps the edge consistent with the fabric rather than producing a line that looks unrelated to it.
Cast off loosely.Use a needle one or two sizes larger in the right hand, or consciously enlarge each stitch before lifting the previous one over. This is what stops the neckband of a jumper being unable to go over a head.
Fasten off properly.Cut the yarn leaving about 15cm, pull the tail through the final loop and tighten. Do not cut it short — you need the tail to weave in.
Weave the ends in along the fabric.With a blunt darning needle, through the back of several stitches, changing direction once so it cannot pull back out. Never knot the ends.
Block the finished piece.Blocking evens out the edges and relaxes the stitches, and it makes both edges look considerably better than they did off the needles.

Tips

Roughly 2.5cm of tail per stitch on double knitting is a reliable estimate.
Cast off with a larger needle. It is the easiest way to avoid a tight edge.
The long-tail cast on counts as row one. Patterns assume you know this.

Common mistakes

Casting off tightly — The cast-off edge has almost no give of its own, so a tight one produces a neckline or cuff that will not stretch over a head or a hand and cannot be fixed without redoing it.
Underestimating the cast-on tail — You discover the shortage after a hundred stitches, and there is no way to add more — the whole cast on has to be undone and started again.

If it doesn't work

Ran out of tail while casting on

Cause: Underestimated the length — Fix: Undo and restart with 2.5cm per stitch, or use a cast on that does not need a long tail.

Cast-on edge too tight

Cause: Loops worked tightly onto the needle — Fix: Cast on over two needles held together, then slide one out.

Neckband will not go over a head

Cause: Cast off too tightly — Fix: Undo the cast off and redo it with a needle two sizes larger, or use a stretchy cast off.

Ends worked loose after washing

Cause: Woven in one direction only — Fix: Weave along several stitches, change direction once, then trim.

Questions people ask

How much yarn should I leave for the tail?

About 2.5cm per stitch for double knitting yarn, or roughly three times the width of the finished piece. Err generously — surplus can be trimmed, shortage cannot be fixed.

Why does my cast-off edge pull in?

Because it was worked tightly. The cast-off row has very little natural stretch, so it needs to be made deliberately loose, usually by working it on a larger needle.