I have found that my quilting fabric widths vary from 40 to 45 inches.
I usually make my first cuts length of fabric - but I usually have larger pieces of fabric available.
If you tell us how much fabric you have - length and width - and what you are trying to cut from it - someone might be able to give you a cutting diagram -
But if you don't have enough fabric to start with (if you need 500 square inches and you only have 400 square inches) - you still won't have enough if you cut it LOF or WOF.
But sometimes that forces creativity and the results are better than the original plan.