Types of Soil: The 12 USDA Soil Texture Classes

The texture triangle

Tap a region to open that class’s page.

How many types of soil are there?

More than one answer, because “soil type” means different things in different systems:

• 3 particles. Every mineral soil is a mix of three separates: sand, silt and clay. They are the building blocks of all the texture classes; see sand, silt and clay.
• 12 texture classes. USDA’s Soil Survey Manual sorts soils by their sand/silt/clay into twelve classes: sand, loamy sand, sandy loam, loam, silt loam, silt, sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay and clay.^[1] This is the system this site maps.
• 12 soil orders. Soil scientists also group soils by how they formed, into twelve orders (Mollisols, Ultisols, and so on); see the 12 soil orders.
• 6 gardening types. The Royal Horticultural Society’s shorthand names six: clay, sand, silt, loam, peat and chalk.^[2] It is UK gardening guidance, not a US or USDA system.

Lists with other counts of soil types are popular but mix these systems together, so we leave those counts aside and stick to the ones a source stands behind.

The 12 texture classes

Download the data (CSV)

The three groups

Our grouping, the same one the calculators use to tailor their guidance.

Six gardening types vs the USDA classes

The Royal Horticultural Society’s six gardening types map onto this site unevenly, because they mix texture with other things. Clay, sand, silt and loam are USDA texture classes (RHS calls clay “heavy,” sand “light,” silt fertile but easily compacted, and loam the balanced mix). But peat is not a texture at all (it is an organic soil), and chalk describes calcium carbonate, what a soil formed over, not its particle sizes.^[2]

Peat and muck are organic soils (Histosols); see organic soils. Chalky soils are alkaline because of their calcium carbonate, a pH matter rather than a texture one.

Soils that don’t fit the triangle

USDA’s survey also maps about 214.9 million acres of miscellaneous areas such as Urban land, rock outcrop and water. They have no texture class and sit outside every figure above.^[3]

It maps about 48.8 million acres of organic soils (Histosols) too: peat and muck made mostly of plant material, which no texture class describes. We count them separately and leave them out of every class figure above, even where a mineral layer lies under the organic surface.^[3][5]

Modifiers and parent material

Two things people call “soil types” sit alongside texture rather than inside it. A modifier such as “gravelly” flags rock fragments without changing the texture class; the thresholds are on the loam page. Parent material is the rock or deposit a soil formed in, such as the wind-laid silt called loess, which the silt page describes.

Soil types for construction

Engineers use a different system again. The Unified Soil Classification System (USCS) groups unconsolidated earth materials by their engineering properties into fifteen groups with two-letter symbols such as GW, GP, SW, SC (“clayey sand”), ML, CL and CH, by grain size and plasticity, not by USDA texture.^[6] USDA soil surveys record a USCS class for each layer, but the size limits differ (USDA sand runs 0.05–2 mm), so the two systems are not interchangeable.

For excavation safety, OSHA classifies soils as Type A, B or C by unconfined compressive strength and condition, with cohesive clays at the stable end and sands and gravels at the least stable.^[7] Each deposit must be classified on site by a competent person, from at least one visual and one manual test. Map data cannot classify an excavation, because the OSHA type depends on strength and conditions that only a site inspection can establish.

Other ways to sort soil

Beyond texture, soils are grouped into 12 soil orders by how they formed, and named individually as series, such as Clarion loam in Iowa. The three particles behind every texture class are sand, silt and clay.

Frequently asked questions

How many types of soil are there?

For texture, USDA uses 12 classes. Soils are also grouped into 12 orders, and individual soils are named as series.^[1][8][9]

What is the most common soil type in the US?

By texture, silt loam: about 33.0% of the mapped US surface soil that has a texture class, in our aggregation of USDA's survey.^[3]

What are the 6 types of soil?

That's a popular simplification: sand, silt, clay, loam, peat and chalk. USDA's texture system has 12 classes; peat is an organic soil, and chalk describes what a soil formed from.^[2][1]

What type of soil do I have?

Enter your address above to see the texture USDA maps there, or test a sample with the jar or ribbon test.