Gauge for substitute yarn

If my yarn says it is 100% cotton and gauge is 3 stitches per inch on a #11 needle but I need a color from peaches and cream brand is 100% cotton and gauge is 4 stitches on #7 needles. My question is how can I see if the peaches and cream will work without purchasing first? Thank you for any help.

You should be able to get 3 sts per inch on 11s with the SnC, it’s a worsted and that’s what I get. But if it’s looser than you like, you’ll have to experiment some. What yarn is in the pattern you’re using?

It calls for Blue Sky Cotton but you need 7 skeins at $11 a skein is a bit too pricey for my purse!

Right, and that’s a worsted yarn too, it’s just knit at a looser gauge. Don’t compare the gauge on the yarn to the gauge on the pattern, compare it to the gauge of the original yarn. It looks like the BS Cotton is also 4 sts per inch on a size 7.