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How Much Topsoil Need Over Gravel to Grow Grass? (Calculator)

How Much Topsoil Need Over Gravel to Grow Grass? (Calculator)

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Do you have gravel in your yard that you’d like to give a different use? Growing grass is an excellent idea. But you’ll have to lay topsoil over this gravel for you to grow grass. But how much topsoil must you lay over gravel to grow grass? 

There’s a formula to determine how much topsoil you need over gravel to grow grass. But ensure it remains at 6 inches deep after laying it over gravel. Generally, grassroots will grow between 4 inches and 6 inches long, so topsoil with this depth is sufficient for your grass to grow healthy. 

Here’s more about adding topsoil over gravel to grow grass that you must know.

Why You Need Topsoil

You could be wondering why you even need topsoil in the first place. Here is where most of the soil actions take place. The beneficial microbes that you need to keep your growing grass healthy dwell in the topsoil. Also, the organic matter decays here. This environment is what the roots of your growing grass need to grow effectively. 

Gravel Preparation

Before laying topsoil over gravel, you must first prepare it. This process is not easy but necessary for the grass to grow healthy. You need to make your gravel smooth and leveled first before anything else using a rake. You should aim to get rid of as much gravel as you can before adding topsoil. 

Also, you wouldn’t want to lose the topsoil over time due to many factors. Therefore, you can add boundaries to the gravel using either cement, rocks, or wood. The border will indeed ensure the retention of topsoil. 

How Much Topsoil You Need for the Project ?

The next step is knowing how much topsoil you need over gravel to achieve the 6 inches depth. The formula used here is straightforward. First, using a tape measure, measure the width and length of your gravel. Then, since you require 6-inches deep topsoil to grow grass, you’ll use the below formula to get how much topsoil you need for this project. 

Amount of topsoil needed=Length X Width X Depth

Length and width, in this case, are the measurements from the gravel, while depth is how deep your topsoil should be, which is 6 inches for grass. For instance, if you have a square gravel measuring 10 feet long and 10 feet wide, then the amount of topsoil you need to grow grass is;

10 by 10 by 0.5= 50 cubic feet. 1 foot is equivalent to 12 inches. 

Topsoil Calculator

Alternatively, you can use any topsoil calculator available online to know how topsoil you must lay on the gravel to grow grass. This is simpler than manual calculation. 

Now that you know how much topsoil you need to grow grass, use a shovel to transfer it to the garden after the above preparation. Then, using a rake, smooth and level this topsoil over the gravel before applying water on it using either a hose and sprayer or sprinkler. Also, you should try as much as possible not to walk on the gravel after preparing and putting topsoil over it to avoid soil compaction. 

Choosing the Right Topsoil

You can purchase topsoil in bulk or smaller quantities that usually come in bags from your local nurseries or garden centers. However, ensure that the water retention of the topsoil you’re buying isn’t so high. This is because laying it over your gravel will produce a high retention effect. 

Consider your climate before purchasing that topsoil from your local vendor. If you come from a very rainy location, sandy, well-draining soil will work perfectly. But choosing such a soil type in a dry environment means constant watering for your grass to grow well. Also, ensure that you’re buying topsoil that is free from all debris. 

You must also add organic matter, such as compost, to this topsoil using a shovel before planting your grass seeds. You can find compost in any garden supply store near you. You need about an inch layer of it spread over topsoil, then incorporate the two using a rotary tiller. Proceed to lay the grass seeds afterward. 


Using the above formula, you can quickly determine how much topsoil you need for the gravel in your backyard to grow grass. However, so you can get it right, you must take accurate measurements of the size of the gravel. Choose the suitable topsoil for your climate and watch as the gravel turns into a beautiful grass garden that you’ve always wanted.

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