Erosion Control Calculator
— How Much Do You Need?

Erosion control refers to the methods and materials used to stop soil from being carried away by water, wind, or foot traffic. When soil erodes unchecked, the consequences can be serious. Slopes lose their stability, drainage channels get clogged, driveways wash out after every heavy rain, and foundations can become undermined over time. Left unaddressed, even minor erosion tends to get worse with each storm. Bulk aggregates like riprap, river rock, crushed stone, drainage stone, fill dirt, and topsoil are among the most reliable long-term solutions available. Unlike temporary measures, stone and gravel do not decompose, they do not need to be reapplied after rain, and they can handle significant water flow when properly sized and installed. Whether you are dealing with a slope in your backyard, a drainage swale along your driveway, or a creek bank on your property, the right aggregate material gives you a durable fix that holds up for years.

The best material depends on where the erosion is happening and how severe the water flow is. Here is how the most common options break down. Riprap is large, angular stone, typically ranging from fist-sized to near-boulder-sized. Its weight and jagged shape make it the strongest choice for areas with fast-moving or high-volume water, like stream banks, steep slopes, and culvert outlets. River rock is smooth and rounded, which makes it visually appealing and a good fit for gentler drainage swales and landscaped areas where looks matter. Keep in mind that its smooth surface means it does not interlock as tightly as riprap, so it is better suited for lower-flow situations. Crushed stone and gravel stabilize driveways, paths, and flat areas prone to surface wash. They compact well and shed water effectively. Drainage stone, sometimes called clean stone or washed stone, is a smaller rounded aggregate with very little fine material mixed in. It is primarily used to manage water movement below the surface in French drains and gravel trenches, reducing the underground pressure that causes soil to give way. Fill dirt and topsoil are used to reshape the land, fill in eroded spots, and establish a base for vegetation, which provides its own long-term protection by binding soil with roots. Many erosion control projects call for more than one material, so do not hesitate to reach out to the Hello Gravel team if you want help choosing the right combination for your situation.

Riprap works by absorbing the energy of moving water before it can tear into the soil beneath. When fast-moving water hits a layer of heavy stone, it slows down dramatically. That slowdown is what prevents soil particles from being picked up and carried away. The angular, irregular shape of riprap is a key part of why it works so well. The stones lock together like puzzle pieces, creating a stable armor layer that resists shifting even under heavy flow. For most residential and light commercial applications, riprap is placed at a depth of 12 to 18 inches. Steeper slopes and channels with faster water flow typically need larger stone and greater coverage depth. Before placing riprap, it is often a good idea to lay down a base of drainage stone or install filter fabric underneath. This prevents a process called piping, where fine soil particles get drawn up through the stone layer and gradually undermine the riprap from below. If you are sizing a riprap project, use the Hello Gravel calculator to get a material estimate based on your specific dimensions. The team can also help you think through depth requirements for your site.

These three materials are sometimes used interchangeably in casual conversation, but they each do something different, and choosing the wrong one for your project can lead to disappointing results. Riprap is angular and jagged. That rough texture is what makes it interlock and hold firm against strong water forces. It is the right call for stream banks, steep embankments, culvert inlets and outlets, and anywhere water moves quickly or in large volume. River rock is smooth and rounded from years of natural water movement. It is attractive and works well in landscaped drainage swales and decorative channels where the water flow is relatively gentle. Because it does not interlock, it can shift under heavy current, so it is not the best choice for high-velocity situations. Drainage stone is a smaller, clean aggregate with minimal fines or dust. It is primarily a subsurface material. You would use it inside a French drain trench, around drainage pipes, or as a base layer beneath other stone to allow water to move freely through the ground. It prevents the underground buildup of water pressure that causes soil to collapse or erode from below. Think of it this way: riprap armors the surface, river rock beautifies gentler channels, and drainage stone manages what is happening underground. A well-designed erosion control system often uses all three in different parts of the same project.

The quantity you need depends on the size of the area you are covering, the depth of material required, and the type of stone you choose. As a general starting point, one ton of riprap covers roughly 15 to 20 square feet at a 12-inch installation depth. One ton of smaller crushed stone or gravel covers approximately 100 square feet at a 4-inch depth. These are ballpark figures because actual coverage varies based on stone size, shape, and density. For a more precise estimate, the Hello Gravel online calculator is your best tool. Enter the length, width, and depth for your project and it will give you a tonnage estimate tailored to your specific dimensions. Getting this right before you order means you avoid either running short in the middle of a project or ordering significantly more than you need. If your project involves multiple areas with different materials or depths, you can run the calculator separately for each section. And if you want a second set of eyes on your estimate, the Hello Gravel team is easy to reach and happy to help you work through the numbers.