Knitting help for a beginner needed!

[teddybearsbear]

Hi

I am looking to knit a simple hat for my baby just a long rectangle which I can then fold over and stitch up I believe it is called a teabag hat

Just wanting some advice on how to work out how many stitches to cast on?

Thanks

[StainlessSteelCat]

Most reliable way is to knit a gauge swatch: www.lionbrand.com/faq/7.html

Briefly:
Using same needles and wool you'll knit the hat in, cast on enough stitches so you will knit more than 10cm. Knit in the same stitch/pattern you plan on using for the hat until you have knitted at least 10cm. Cast off. Lay your swatch flat, pin down and measure out 10cm along a row, mark with pins. Count up how many stitches you have in 10cm, this is your gauge.
Measure your baby's head, divide that by 10 and multiply by your gauge. Cast on this many stitches, add 2 for the seam and knit. If you are using a pattern, you can fudge the exact number so get a multiple of a repeat if you need to.