How long should the remaining thread be for weaving in the ends?

Dear users, dear authors,
once your knitting or crochet project is finished, how long do you leave the yarn before cutting it and weaving in the ends? How do you go about sewing it in?

It depends on what I’m crocheting. For amigurumi, for example, which consist of several parts, the end of the yarn can still be used to attach the head or limbs. In that case, I leave it longer—about 20–25 cm, depending on the size of the part being attached. Otherwise, about 10 cm. It’s better to leave it a little longer and cut it off after sewing than to leave it too short and have the piece come undone.
When sewing with a sewing machine, the thread can be cut very short right away if you “lock” the beginning and end of the seam—that is, sew backward over it again.

When sewing by hand, I find that a length equal to the needle’s length is enough to weave in the ends—it works just fine, and you get the hang of it with practice :-) Otherwise, I do it like Ruth: I leave a length depending on what else I want to or can do with the yarn.

Best regards, Inge

I leave the starting and ending yarn tails a little longer and then use them to sew my work together. 

Right now I’m working on baby shoes with one seam. For that, I use the remaining tail from the cast-on to sew them together.