How to use the soil texture class calculator
- Choose Sand, silt, clay % or Jar test layer depths.
- For percentages, enter the sand and clay. Silt can be left empty and is found as the rest, or you can enter all three.
- For a jar test, measure the depth of the sand, silt and clay layers after they settle and enter the three depths in any one unit.
- Read the texture class, the percentages and a short description of the class.
Formula
Percent = layer depth / total depth x 100 (jar test)
Silt = 100 - sand - clay when it is left empty
Class from the USDA texture triangle: the sand, silt and clay percentages fall into one of twelve regions
Example region: clay of 40 percent or more with silt of 40 percent or more is silty clay
The twelve classes are sand, loamy sand, sandy loam, loam, silt loam, silt, sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay and clay. Every set of three percentages adding to 100 falls in exactly one of them.
Three samples
60 percent sand, 20 percent silt and 20 percent clay is a sandy clay loam, not a sandy loam, because the clay reaches 20 percent. 40 percent sand, 40 percent silt and 20 percent clay is a loam.
A jar test with layers of 30 mm of sand, 20 mm of silt and 10 mm of clay gives 50 percent sand, 33.333 percent silt and 16.667 percent clay, which is also a loam.
Doing a jar test
Fill a straight-sided jar about a third full of soil, add water almost to the top and a drop of dish soap, and shake it well. Sand settles in about a minute, silt in a few hours and clay in a day or more. Measure each layer after it has settled, then enter the depths. The result is an estimate, because organic matter floats and fine clay can stay cloudy.
Once you know the texture, plan a bed with the raised bed soil calculator and the plant spacing calculator. The VPD calculator and the EC to ppm calculator cover growing conditions.
Why the class matters
Texture affects how fast water drains, how much a soil can hold and how easily roots move through it. Sandy soils drain quickly, clay soils hold water and nutrients but can pack down, and loam is a balanced mix. A class name is a starting point for choosing what to add, and a laboratory test gives a firmer answer.
Assumptions and limits
- The classes follow the boundaries of the USDA soil texture triangle for particles under 2 mm.
- A point exactly on a boundary goes to the class that includes that edge, so a tiny change can move it to a neighbor.
- Sand, silt and clay must add to 100 percent, within half a percent when you enter all three.
- A jar test is rough, and a laboratory analysis gives more reliable percentages.
Frequently asked questions
How do I find my soil texture?
Measure or estimate the percentages of sand, silt and clay, then find the region of the USDA triangle they fall in. A jar test gives a rough estimate at home.
What is loam?
It is a soil with a fairly even mix of sand, silt and clay, with clay between 7 and 27 percent and silt between 28 and 50 percent in the USDA system.
Why did 60/20/20 become sandy clay loam?
In the triangle, a soil with 20 percent clay and less than 28 percent silt with more than 45 percent sand falls in sandy clay loam, even though sand is the biggest part.
Does the class tell me what to plant?
No. It describes the mix of particles. Fertility, acidity, organic matter and drainage also matter, and local advice for your crop is the better guide.