I am no upholstery wiz. I leave the big stuff to the professionals. But no-sew little seat cushions, no problem. I showed you my neighbors new/old breakfast area dining set here. Now, here is how we covered those seats.
This is what the chairs looked like before:
My neighbor had done her homework and bought 2 inch foam padding for the seats and cut them to size. We glued the foam to the old woven seats.
Then we laid out the fabric and measured. With the 2 inches of foam, the 1 inch of the original seat and at least an inch to staple, we needed to cut our squares with an additional 4 inches on each side of the seat.
I am an advocate of measuring twice and cutting once! I am also an advocate of cutting squares, not cutting to the shape of the object being covered. Why, you ask? Because you can always trim excess fabric but you can’t put it back on!
That’s my neighbor, cutting away!
Now, you lay the seat with the foam on top, foam side down, and pull up one side of the fabric. Then you staple it into place. Then you pull the fabric from the opposite side nice and tight and staple into place. I do opposite sides so that the fabric gets pulled very tight and looks nice and smooth.
Keep the staples close together so that the fabric stays stretched. You can replace the cushions on the chair frames and voila! It’s just like new!