How much yarn do I need if making the pattern larger?
I am making a blanket for my daughter and the pattern says that you can easily make the blanket larger by casting on more stitches in multiples of four and by adding extra rows. I purchased one extra skein of yarn to make this blanket and I'd like to use it all so I'd like to increase the width and length for one skein's worth. To give you some details, the gauge is 21 sts and 28 rows to 4in/10cm over cell st pattern using size 5 (3.75mm) needles. The finished size of the blanket should be 26 3/4in x 35 1/2in (68cm x 90cm) using 7 skeins. I will be using 8 skeins. The yarn is Rowan Milk Cotton which is 124yd/113m per ball and 1 3/4oz (50g) per ball.
The pattern asks to cast on 69 stitches. I was thinking of increasing by 8 but please let me know if you think I might run out of yarn.