How much yarn

The pattern I am making calls for 1600 yds of worsted wt yarn, at 4.5 sts per inch for my size.
I want to use a yarn that knits up at 3.75 sts per inch, a chunky wt, is there a way to figure how much of the chunky wt yarn I would need to make the pattern?

If you divide the recommended yardage by the recommended gauge that gives you a factor of 1600/4.5 = 355.55.

Now if you multiply your gauge of 3.75 by the factor of 355.55 that gives you just a hair over 1333 yards.

This site has some basic sweater patterns that follow the Elizabeth Zimmerman formula. In the reference section there is a button that helps you calculate how many skeins.

Thank you for the information, now I know I have enough yarn to continue.