Hi and welcome to KH.
Sometimes if the pattern is written for different sizes, you can make a different size with heavier yarn and it will come out right. Sometimes you can just adjust the number of stitches used. How complicated is the pattern? Does it have cables or something? What's it called? If we know the name of the pattern and the book it's in, we might find a picture online or someone else may actually have the same pattern.
I should never overestimate my basic arithmetic skills.