With Variants (Products having a different price, etc.) you specify the weight in ounces in the Variant details.
This is the formula for setting up the Variant details:
You specify the 3 "Option Values".
Make sure you've entered the correct weight in ounces in the details. For example, if you are selling shoes that are $25, weigh 3 oz, you have 50 in stock, Option1Value is Color, Option2Value is Style, and Option3Value is Size... Your Variant details should look something like this: