How many should o cast on

im knitting a simple all knit scarf with size 8 needles. How amnt should i cast on?

It depends on how wide you want it and your own tension. Since garter stitch is easy and quick try casting on 30 and knit for an inch or two and see if that’s wide enough. If not take a look at how wide 5 stitches are on the needle and add or subtract accordingly.

You should go by eye, casting on according to how wide you want the scarf to be. Although I have found that casting on to get a certain width always gives me much more width than desired, so maybe you should cast on a little less than the desired width.

The cast on will usually measure about 80% of what the actual width turns out to be. So if you want an 8" wide scarf, you’d cast on about 5" of stitches.