There are 3 feet in a yard, so a square yard = 3 feet X 3 feet = 9 square feet. Since your frame is 3 feet by 8 feet, 3 X 8 = 24 square feet. Divide 24 square feet by 9 square feet = 2 2/3 square yards.

But more importantly, you'll probably want to cover your frame with a single piece of fabric. If you choose fabric that is 3 feet wide, will you have enough fabric at the edges to attach to the frame? If so, buy 3 yards of 3 foot wide fabric and you'll be fine. But if you need extra to attach to the edges of the frame, buy 4 foot wide fabric instead. In that case, buy 4 yards of fabric in order to have enough to make the 8-foot length of the frame (with some fabric left over.)

If you Google " convert 8 feet x 3 feet to square yards " and it will tell you - you probably won't even have to come out of Google as the answer may already be displayed as it was on my search. If not go to the conversion site Google recommends and put the same question. The answer, obtained in seconds is 2.66666667 square yards.

3 ft. x 8 ft. = 24 square feet.

But since most fabric is 44 inches wide, you would probably need about 3 yards.

45" or 60 inch wide fabric? and does it need to be ONE unseamed piece? 45 inch 2 2/3 yard would be one piece with 9" to trim off on edges

You aren't dealing with inches. 3 feet is one yard - multiplied by 8 feet = 24 square feet.

how many feet in a square yard - 3 X 3 = 9.

So 24 divided by 9 ......... or........ 2.666 yards.

I am assuming this is a plain fabric - if patterned you have to take the pattern

'drop/repeat' into the equation.