I received a sample of a red tartan fabric from SMS Auto Fabric and while it is not an exact match of the original, it looks pretty good! Anyone know how many yards of fabric are needed to cover a seat insert?

I'm sorry that I don't know off of the top of my head, but I do know that 1 yard of upholstery fabric or vinyl is 54" X 36". Both of my parents are upholsterers, I will typically measure all the pieces and try to fit them on an imaginary 54" wide X ? area to figure out how many yards I need.
Don't forget to include enough for the seams, and vinyl stretches lengthwise so you'll need to cut some parts that may fit crosswise lengthwise instead so that you can use the stretch to your advantage, and fabric has a nap like carpet so you'll need to match the nap between insert pieces or it will look like different colors.

If you are doing the centers and bottom of the seat you can probably scrape by with a little more than one yard. I would get two in case of goof ups. Will you do the door panels too? Dash face?

I just finished (mostly) redoing my interior from scratch. Frustrating but rewarding.

Redoing the entire interior but the plaid is for the seats only. Thanks for inupt!