Things You'll Need
While most patterns will clearly state how much fabric is needed, you may occasionally stumble across one that does not. If this happens, you'll need to calculate for yourself how many yards of fabric are needed to finish the pattern. Most fabric sold by the yard is either 45 or 60 inches wide, so check to make sure how wide the fabric you're thinking of using is before you perform your calculations. Not all patterns can be done with the narrower 45-inch-wide fabric.
Cut out all the pieces of your pattern.
Decide whether you'll be using fabric that is 45 inches wide, 60 inches wide, or a custom width such as 42 inches.
Cut two pieces of string that are at least 5 feet long. Lay them out as straight as you can, parallel to each other, and as far away as the fabric you've chosen is wide. For example if you're calculating how many yards of 45-inch-wide fabric are needed, your strings should make two straight parallel lines 45 inches apart.
Lay all the pieces of your pattern out between the strings. If any of the pattern pieces overlap the strings, try orienting them differently to make sure they fit within the strings. If they still overlap, you need to base your calculations on a wider fabric and adjust the strings accordingly.
Make sure that you've left plenty of space between your pattern pieces for cutting and for seam allowances, but otherwise try to group them as close together as possible. The less empty space you leave between the strings, the more efficient your use of fabric will be, and the more money you'll save.
Add more string, laid down over the previous strings, to extend the borders of your pattern area if the initial layer of string wasn't long enough to stretch the length of all your pattern pieces laid out.
Rip off a small piece of masking tape and place it on one piece of string, about 2 inches beyond the leftmost edge of the leftmost pattern piece. Do the same thing to mark a spot about 2 inches beyond the rightmost edge of the rightmost pattern piece, making sure to mark both locations on the same piece of string or pieces of string laid out together.
Measure between the two pieces of tape. This is how many yards of fabric you will need to complete your pattern.