how much fabric to cover sport seat?

[85.5classic]

I need to recover my sport seats(2) with cloth. I will only need to do them as pictured. The black vinyl will stay.

[ddbach]

The plaid has a pattern repeat so may require more yardage. Think of wallpaper. The side bolsters are cut on a bias (45 degree angle) for better stretch and to conform to curves which definitely needs more yardage. If the fabric has a bit of a nap you need to keep all pieces oriented the same direction or they will feel/look different. Also adds to yardage. Don't forget a seam allowance, better too long than too short. Finally also depends upon how wide the weavers are making the cloth. Upholstery fabrics generally come 54in wide, some automotive 62in wide, this can change your yardage a small amount.
That said I would guesstimate at 5 to 6 yards after rough measuring my seats. Best bet ask someone who has experience with reupholstering furniture or better, car seats. DIY - make patterns with clean newspaper or tissue marking plaid pattern and layout on a grid then measure area used.