Fabric, vinyl, and Ultraleather come on rolls, and are measured by the running yard, which is 36" by 54". That is 3 ft. by 4 1/2 ft. or 13.5 square feet per yard. When I do a layout, I have a general idea how big each of the parts are beforehand, draw them in on a piece of paper, and move them around until I get the best yield. I do this before I order the fabric. If you want to use graph paper to do a layout, that might help you. Be generous
in your estimates, it's better to have too much fabric than too little, especially if you make a mistake along the way.
In general, a pair of bucket seats will take 3 yards for both seats. A rear bench seat will take 2 1/2 to 3 yards. Two door panels, two kick panels, and two sun visors will take 2 yards for all six pieces, and a headliner will take 5 yards if it is a bow type headliner on a full size car. These figures are for a one fabric interior. If you are going to two tone the door panels and seat covers, you will have to also figure out how much of the second fabric you will need.
Remember that all the pieces need to be laid out in the same direction, and that could be down the roll (left to right, or railroaded) or across the roll (top to bottom, or non-railroaded). This is true for fabric to keep the nap all going the same direction, and even for vinyl or Ultraleather to keep the stretch of the fabric all going in the same direction. I usually lay fabric out so that all the nap on all the pieces is smooth to the right. It doesn't really make a difference if the parts are left to right or right to left, but that's how I learned, so that's how I do it. If your headliner has large pieces, bigger than 54" wide, you need to lay the fabric out down the roll so all the parts are cut from one piece of fabric. If you have to lay the headliner out down the roll, then lay everything else out down the roll. Good luck. If you have any more questions, just ask.
No one lives forever, the trick is creating something that will.