Types of Gravel: A Complete Guide to Different Grades and Uses

Gravel is a versatile material — it can be used for decorative purposes, like adorning flowerbeds or garden paths, or in more practical ways, to pave a driveway or a walkway. But not all gravel is the same. If you want to start a landscaping project, you need to know that there are many different types of gravel to choose from. These vary not only in size but also in shape and purpose.

Don't worry — we are here to explain everything! This guide will help you understand gravel in more detail and learn about different kinds of gravel and their grades so that you can choose the right one for your project.

Before we talk about the different types of gravel, let's first understand what gravel is. You probably already know that gravel consists of small, loose rock fragments no larger than a few dozen millimeters. In everyday life, all kinds of coarse soil are commonly referred to as "gravel"; however, you have to know that there are two different types of loose stones:

• Gravel, which forms naturally through weathering and erosion; and
• Crushed stone, produced mechanically by crushing larger rocks. Just like in the case of gravel, there exist different crushed stone types, which we will talk about in the following sections.

The International Organization for Standardization (ISO) defines gravel as a type of coarse soil made up of rock fragments measuring 2-63 mm (~ ¹⁄₁₆"-2½"). Anything finer is considered sand 🇺🇸 or dust; anything coarser is cobble or boulder.

In some parts of the world, the definition may differ — e.g., according to the Unified Soil Classification System (USCS), gravel measures 4.75-76.2 mm (~ ³⁄₁₆"-3"), while the American Association of State Highway and Transportation Officials (AASHTO) defines gravel as soil containing particles between 2 and 75 mm (~ ¹⁄₁₆"-3").

Nevertheless, gravel can measure up to around 100 mm (~4") in accordance with industry standards.

Gravel grades and sizes are two strictly related concepts — each gravel grade corresponds to a range of sizes of gravel, and the bigger the grade, the smaller the stones. In the United States, grades are based on AASHTO M43 (Standard Specification for Sizes of Aggregate for Road and Bridge Construction) and ASTM D448 (Standard Classification for Sizes of Aggregate for Road and Bridge Construction).

The grade itself is determined by the size of the sieve used to measure the particles, as only fragments of a specific size will pass through the mesh, for example:

• #1 – 2"-4" (~50-100 mm)
• #2 – 1½"-2½" (~38-63.5 mm)
• #3 – 1½"-2" (~12-50 mm)

...and so on.

As you can see, the grades used in the US overlap, as they also depend on the percentage of stones of a specific size that pass, while the rest become trapped by the metal mesh. If you want to know more about gravel grades, how they overlap, and what they are typically used for, take a look at our dedicated article, Gravel Size Chart: Understanding Gravel Sizes.

Grades and gravel sizes are not the only characteristics used to classify this material — its optimal use will also vary depending on its source and the properties of the stone. We have prepared two tables presenting some of the most commonly used gravel and crushed stone types, sizes, and uses.

Gravel types

Crushed stone types

Of course, let's also not forget the other part of the gravel market: crushed stone.

Washed vs. unwashed gravel

When choosing the right gravel types for your projects, remember that gravel can be washed or unwashed.

• Washed gravel — This gravel type has been screened and washed to remove fine particles. It is less compact but more aesthetic and better for drainage. It is often on the expensive side.

• Unwashed gravel — A "dirty" type of gravel, which is mostly unprocessed, therefore contains considerable amounts of sand, clay, and/or dust. It is the best for road bases, foundations, and fill, as it compacts well.

  However, you should think twice before choosing unwashed gravel for your pathways — it will compact quickly, but the finest particles will lift up when walked over. It is also unsuitable for drainage layers.

We hope that you can now fully appreciate gravel's amazing qualities! Not only is it practical and useful, but it's equally valued for its elegance and charm. Different needs will call for different kinds of gravel — sometimes, we'll need pea gravel to decorate our decking 🇺🇸, other times, we'll use river rock to create a drainage layer under our garden; unwashed gravel will be great for fills, but we'll have to buy washed gravel if we are planning a landscaping project.

The possibilities are endless, and we hope that this guide will help you confidently carry out any gravel project!