I had been looking for outdoor pillows in the shade of green that I ordered here, for a while, and in the size range that would fit my bistro set chairs. The perfect size would have been 19" square, but when I found these that were 18" I ordered them anyway - since they were the right color and materials. In reality they are closer to 17" wide, unless you measure along the edges where the corners add to the measurement. But certainly not enough reason to return them. They just won't fit anywhere near snuggly in the seats the way that I envisioned, but they do look good, and will stilI be cushy to my tushy. (FYI) There are no ribbons to anchor them to the chair, which I knew, but there is a tag on one corner that can be used to attach your own, without compromising the pillow cover itself.