Outline the garden's perimeter, using either a rope or a garden hose. If you are creating a new garden, make sure the size and location is suitable for the plants it will contain. If you are edging around an existing garden, wrap the hose or rope around the garden's perimeter.
Stretch out the garden hose or rope and measure the length used to wrap around the garden bed.
Take this measurement to your local gardening center. Select the round edger that appeals to you and measure its width. Divide the edger's width by the garden's perimeter. For example, if the edger is 7 inches wide and the garden bed is 320 inches around, you will need 46 round edgers.