I've been on the hunt for a new pool cover that fits our existing anchors. It is maddening how few vendors include these measurements in their listings! So I'm here to tell you: the strap spacing for a 20x40 pool is 5 feet 4 inches. Most of our existing anchors are 5 feet 3 inch, the rest are 5 feet 4 inch. I don't know why the discrepancy; we didn't install them. However, this cover works perfectly despite the small variation. There are 9 straps on the long sides, and 5 on the short ends. I think the neighbors thought I was laying eggs when I discovered this would fit perfectly, but no, I was celebrating how I got it right on the first try ordering something online blindly.