Gravel Size Chart: Understanding Gravel Sizes

Are you starting a construction project and have no idea what gravel you should use? You're in the right place! In this article, you'll find a practical guide to gravel grades and sizes. We have prepared a gravel stone size chart to help you discover the most common gravel grades and their size ranges. This guide will show you gravel sizes with pictures and explain the most common uses for each grade.

You probably already know that gravel and crushed stone are materials consisting of small stone fragments used in construction and decorative landscaping. But how do we classify gravel?

Gravel grades

In many parts of the world, but especially in the U.S., gravel and crushed stone are divided into grades corresponding to specific size ranges. These help engineers and landscapers choose the right aggregate for each project. Each grade is determined by the sieve size used to measure how much of the material passes through.

American construction companies often refer to the norms defined by AASHTO M43 and ASTM D448, which specify sieve sizes used for measuring gravel particles. Some grades are larger, therefore, more suitable for drainage systems and erosion control, while others are small and visually appealing, perfect for decorative purposes.

Where do gravel grades come from?

Hurray, now we know what gravel grades are, but what do those numbers really mean? Well, it's not just a casual, linear series of numbers: depending on the system used, they are based on the size or number of openings in sieves.

• AASHTO M43/ASTM D448 — If you are using the American system, the grade numbers are tied to the number of openings per inch — for example, #4 means the particles need to pass through a sieve with 4 openings per inch.
• ISO 14688-1:2017 — The sieve sizes that follow the European system might seem a little bit odd and random: you will notice values like 6.3, 2, 63, 20, etc. These are based on a geometric progression with a ratio of ~1.25; therefore, the scale-up between each grade is very consistent, about 25% larger than the previous one.

How do we determine the grade of our material?

We all like pretty, polished, uniform gravel; however, not everything is clear-cut. Gravel grades are not based on the size of a single sieve, but rather on the amount of gravel that passes through a set of sieves. This amount is measured as a percentage of the total weight of the material.

AASHTO defines specific ranges for each of the grades, but the generalized pattern would be as follows:

• 100% passes through a sieve ∼2x the average nominal size (this is called maximum size);
• 90%-100% passes through ∼1.5x the average nominal size;
• 35%-70% passes through the average nominal size;
• 0%-15% passes through ∼0.5x the average nominal size;
• Only up to 5% can pass through #200 for cleaner stones.

Remember that this is only a "rule of thumb"! For instance, let's look at #3 gravel (½"-2" nominal size), which is defined as follows:

• 100% passes the 2" sieve
• 90%-100% passes the 1½" sieve
• 35%-70% passes the 1" sieve
• 0%-15% passes the ½ sieve

Special gravel grades

Apart from the basic grades, usually going from #1 to #10, there are also blended grades, such as #21 and #411, which are both types of crusher run, creating a dense aggregate containing a mixture of stones and fine particles. These allow the gravel to compact, which makes it perfect for creating a stable surface, such as a road.

We hope you now have a clear picture of how gravel grades work, so why don't we look at some examples?

We have created a chart containing the most commonly used gravel sizes with pictures. For each grade, you'll discover what that particular grade looks like and what it is most often used for. Whether you need big, chunky stones that hold up roads, or some fine gravel to smooth out your driveway, use this little cheat sheet to compare sizes and pick the gravel that will work best for you. You can then head to our complete guide to different gravel types and uses to choose the right gravel type!

As you can see, gravel grades are a pretty convoluted concept. Not only are there multiple classification systems, but also certain grades overlap, making it harder to distinguish between them and choose the right one. Whether you are paving your driveway or want to create a compact road, we hope that, thanks to our gravel stone size chart, you won't have any issues picking the right gravel grade.