100gram is about 60 meter, it varies a bit per skein
This recycled sari silk ribbon is a delicate yarn. We use it to weave or to crochet around the yarn "crochet weaving" For knitting we found it not always strong enough. You could try to reinforce it with another yarn that has no stretch.
I made a little simple sample loom to find out how much yarn you need for weaving. The nails are 1cm apart from each other. For a 10x10cm sample I used 15 gram.
So for a 50x50 cm pillowcase you will need 375 gram (4 skeins of 100 gram)
The sample pictures were used with a different colour of the same yarn which is unfortunately out of stock