Pea gravel is relatively cheap ground cover. It's recommended that you make the pea gravel 2″ thick. A ton of gravel will cover about 100 square feet, 2″ deep. Typically gravel is sold by the ton or scoop, and a scoop is usually equivalent to a ton. We used pea gravel in our raised bed garden for drainage in the pathways because it was much cheaper than using bark or mulch.