Gauge help needed...grace vs. worsted

I have a summer top pattern that I’d love to knit, however it calls for worsted weight yarn. It’s pattern states a gauge of 20 sts and 26 rows = 4 inches or 10 cm in st st…I have a bunch a Grace cotton yarn that someone gave me. It is a lot thinner and has gauge with size 4 mm (US 6)
needles = 24 stitches = 4 inches or 10 cm. but I really want to use this Grace and was wondering how I could use it in this pattern…could I use double the strand of yarn or make the pattern a larger size/smaller…I’ve always been terrible at the conversion stuff???Any ideas you could give me would be great…thanks so much!!!

Double stranding the yarn would make it much too thick, like a bulky weight, but you can make a larger size of the pattern without too much hassle. Knit up the Grace on size 6s and see what your sts/inch are. Then multiply that by how many inches around you need, and find the pattern size that’s closest to that many sts. Follow the st instructions for it, adjusting the length to your correct size.

Yarn Conversion Help Please!
I have an old Shawl pattern that I would like to knit (the picture of the woman modeling it makes me think '40’s or 50’s). It call for 20 oz of Bulky Yarn knit on size 11 needles with no gauge, only states that it is 64 inches in length and no width. I would love to knit this in a softer lighter yarn. Are there any charts that would help me make this work? Or, can someone help me with suggestions.

I would figure out how many stitches make up the repeat if any. Usually there will be several edge stitches with the pattern in the middle. You can increase the number of pattern repeats to reach the width you want and then just continue knitting until the length you want.