A soil texture triangle is a diagram that tells you your soil type based on the percentages of sand, silt, and clay it contains. Each corner of the triangle represents 100% of one particle type, and the interior is divided into regions representing 12 official soil texture classes. Reading it comes down to finding three lines on the triangle, one for each particle size, and seeing where they intersect.
What the Three Sides Represent
The triangle has three axes, each scaled from 0% to 100% for one of the three soil particle types. Sand particles range from 0.05 to 2.0 millimeters in diameter, silt particles from 0.002 to 0.05 mm, and clay particles are anything smaller than 0.002 mm. Your three percentages must add up to 100%, since every grain of soil falls into one of these three size categories.
On a standard USDA soil texture triangle, the bottom axis shows sand percentage (reading left to right), the left axis shows clay percentage (reading from bottom to top), and the right axis shows silt percentage (reading from top to bottom). Different versions of the triangle may arrange or label these slightly differently, so always check which particle is on which side before you start.
How to Plot Your Soil Sample
Say your soil sample is 40% sand, 30% silt, and 30% clay. Here’s how to find where that lands on the triangle:
- Start with clay. Find 30% on the clay axis (left side). Follow the horizontal guideline that runs from left to right across the triangle at the 30% mark.
- Next, find silt. Locate 30% on the silt axis (right side). Follow the guideline that angles down from upper right to lower left.
- Check with sand. Find 40% on the sand axis (bottom). Follow the guideline that angles up from lower right toward upper left.
All three lines will cross at a single point. The texture class region where that point falls is your soil type. In this example, the intersection falls in the “clay loam” zone. You only technically need two of the three lines to find the intersection, since the third percentage is determined by the other two (they must total 100%). But tracing all three is a good way to double-check your work. If the three lines don’t meet at the same spot, one of your percentages is off.
The 12 Soil Texture Classes
The triangle is divided into 12 named regions. These range from the three extremes (sand, silt, and clay) to various blends. The full list of USDA texture classes is: sand, loamy sand, sandy loam, loam, silt loam, silt, sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay, and clay.
“Loam” sits near the center of the triangle and represents a fairly balanced mix of all three particle sizes, roughly 40% sand, 40% silt, and 20% clay. It’s often considered ideal for gardening because it drains well while still holding moisture and nutrients. Soils named with modifiers like “sandy clay loam” lean toward the characteristics of those particle types. A soil classified as “clay,” for instance, contains at least 40% clay particles and will feel sticky, drain slowly, and hold nutrients tightly.
Some regions on the triangle are large (sandy loam covers a wide range of combinations) and some are small (silt is a narrow sliver requiring at least 80% silt with very little clay). The boundaries between classes aren’t gradual transitions in reality, but the named zones give you a practical shorthand for how your soil will behave.
How to Get Your Percentages
You need the sand, silt, and clay percentages before you can use the triangle. There are two common ways to get them.
The simplest home method is the jar test. Fill a straight-sided jar about one-third full with soil, add water until nearly full, then add a teaspoon of dishwasher detergent or water softener to help separate the particles. Shake thoroughly and set the jar on a level surface. Sand settles first, so mark the top of the sediment layer after one minute. Silt settles next; mark that layer after about six hours. Clay takes up to 24 hours to fully settle. Measure the height of each layer, divide by the total sediment height, and multiply by 100 to get your percentages.
For more precise results, the USDA’s Natural Resources Conservation Service offers a free online Soil Texture Calculator. You enter your particle percentages and it returns the texture class automatically, no triangle-reading required. Web Soil Survey, another NRCS tool, can tell you the mapped soil types for any address in the United States, which is useful if you want to know what’s under your feet before you start digging.
Reading Tricky Intersections
Sometimes your point lands right on or very near a boundary line between two texture classes. This is normal. Soil texture exists on a continuous spectrum, and two soils on either side of a boundary line will behave almost identically. If you’re on the edge between, say, loam and clay loam, either label is a reasonable description of your soil.
Keep in mind that the jar test and even lab methods have some margin of error. A result of 26% clay versus 24% clay could place you in different classes on the triangle, but the practical difference in how that soil holds water, supports roots, or needs amendment is negligible. The texture class is a starting point for understanding your soil, not a precision measurement.
What Your Texture Class Tells You
Once you’ve identified your soil type, you can make informed decisions about drainage, watering, and soil amendments. Sandy soils drain fast and dry out quickly, so they need more frequent watering and benefit from added organic matter to hold moisture. Clay-heavy soils retain water and nutrients well but can become waterlogged and compacted, making them harder for roots to penetrate. Silty soils hold moisture better than sand but are prone to erosion and surface crusting.
Loamy soils, and the various loam blends near the center of the triangle, strike a balance between drainage and water retention. If your soil falls in one of the extreme corners, amendments like compost, peat, or coarse sand can shift its behavior closer to that balanced center. The triangle won’t tell you about your soil’s pH, nutrient content, or organic matter, but texture is the single most stable physical property of soil and shapes nearly everything else about how it performs.