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Soil Jar Test Calculator

A quart jar, water and a teaspoon of detergent will separate your soil into sand, silt and clay. Measure the layers and this calculator gives you the percentages and your USDA texture class.

Enter the thickness of each settled layer. Any unit works (in, cm or mm).

Your soil texture result is ready.

sandloamysandsandyloamloamsiltloamsiltclayloamsiltyclayloamsandyclaysiltyclayclay202020404040606060808080Sand %Silt %Clay %

Sandy clay loam

Your USDA texture class

sandy clay loam

60% sand · 10% silt · 30% clay

20–35% clay, over 45% sand.

With 20% clay or more, these soils behave as sticky, gummy clayey soils.

  • At 30% clay, expect clay-like behavior: Colorado State University Extension notes that a soil with as little as 20% clay can behave like a clay soil.

Each percentage is a layer's thickness divided by the total; classes use the USDA Soil Survey Manual boundaries. How we calculate this.

Compare with your mapped soil

See USDA's mapped topsoil texture for an address next to your jar result.

US addresses only: street address, city and state, or ZIP.

A soil jar test separates soil by settling. Sand drops out in about a minute, silt in about two hours, and clay only when the water clears, usually 1 to 3 days[1]. Each layer’s thickness divided by the total gives its percentage, and the USDA triangle turns those into a texture class[2].

What you need

  • A tall, straight-sided jar with a tight lid (a quart mason jar works)
  • Dry soil from the spot you want to test
  • Water
  • Powdered, non-foaming dishwasher detergent
  • A ruler and a marker

Straight sides matter: when the jar’s width doesn’t change, each layer’s height is proportional to its volume.

Step by step

These are Colorado State University Extension’s steps[1].

  1. Dry the soil on newspaper, pick out rocks, roots and debris, and crush the clumps.
  2. Grind it finely.
  3. Fill a tall, straight-sided jar (a quart jar works) one-quarter full with the soil.
  4. Add water until the jar is three-quarters full.
  5. Add a teaspoon of powdered, non-foaming dishwasher detergent.
  6. Close the lid tightly and shake hard for 10 to 15 minutes to break the soil into single particles.
  7. Set the jar where it won't be disturbed.
  8. After 1 minute, mark the top of the settled layer; that's the sand.
  9. After 2 hours, mark the top again; the new layer is silt.
  10. When the water turns clear (usually 1 to 3 days, sometimes weeks), mark the top of the clay.
  11. Measure each layer and enter the numbers below.
waterclaysiltsand

1 minute → sand · 2 hours → silt · 1–3 days → clay (sometimes weeks)[1].

Why the layers separate

Particles settle out of the water by size[1]. Sand grains, up to 2 mm across, reach the bottom first; clay particles, under 0.002 mm, settle last[2]. Soil labs measure the same thing more precisely with a hydrometer, from the different settling rates that Stokes’ law describes[3]. Our guide to sand, silt and clay explains that lab method.

The same jar after about a minute, after about two hours and once the water clears: sand, then silt, then clay, with bits of organic matter floating on top.

Bits floating on the water are organic matter, which is good for your soil[4]. Leave them out of the measurement: the test reads only the settled sand, silt and clay, which is why the steps start by picking out roots and debris[1].

Worked example

Colorado State University Extension’s worksheet example: sand 3.0 in, silt 0.5 in, clay 1.5 in[5]. The total deposit is 5.0 in, so sand is 3.0 ÷ 5.0 = 60%, silt is 10% and clay is 30%. On the triangle that’s sandy clay loam[2]. Measured as jar marks instead (3.0, 3.5 and 5.0 in from the bottom), you get the same result.

Load this example

Got your percentages? Learn how to read the triangle by hand, or print a worksheet for the classroom.

Example readings and their classes

Each row is classified with the Soil Survey Manual’s class definitions[2].

Sand · Silt · Clay (in)Sand % · Silt % · Clay %Class
3 · 0.5 · 1.560 · 10 · 30sandy clay loam
2 · 1.5 · 0.550 · 37.5 · 12.5loam
1 · 2 · 125 · 50 · 25silt loam
4.2 · 0.5 · 0.384 · 10 · 6loamy sand
1.5 · 1 · 2.530 · 20 · 50clay

Getting a reliable result

  • Dry the soil and crush the clumps before it goes in the jar.
  • Shake the full 10 to 15 minutes; the shaking breaks the soil into single particles[1].
  • Don’t move the jar while it settles.
  • Wait until the water is clear before marking the clay. That’s usually 1 to 3 days, and some soils take weeks[1].

Jar test, ribbon test or lab?

The jar test gives numbers, but Colorado State presents it as a way to estimate texture[1]. The ribbon test is quicker and gives a class without numbers.

For exact figures, a soil lab runs a particle-size test that reports the sand, silt and clay and the USDA texture class; Penn State’s Agricultural Analytical Services Laboratory is one that offers it[6].

Ways people use the jar test

  • Before planting a new bed: know whether you’re starting from sand, loam or clay.
  • Checking a load of topsoil before you spread it.
  • A school science project: the layers are visible within hours, and the calculator turns them into a real USDA class.
  • Comparing your garden with USDA’s mapped soil for your address.

How we calculate this

In layer mode, each percentage is that layer’s thickness divided by the sum of all three. In jar-mark mode, sand is the first mark, silt is the second minus the first, clay is the third minus the second, and the total is the third mark. Percentages are rounded to one decimal and kept summing to 100, then classified with the Soil Survey Manual’s class definitions[2], the same rules as the texture triangle.

Frequently asked questions

How long does a jar test take?

Sand settles in about a minute and silt in about 2 hours. Clay takes until the water clears, usually 1 to 3 days, sometimes weeks[1].

How do I calculate the percentages?

Divide each layer’s thickness by the total thickness[1]. In Colorado State’s worksheet example, 3 in of sand in a 5 in deposit is 60% sand[5].

What does a mason jar soil test tell you?

The share of sand, silt and clay in your sample, and from those its USDA texture class[1]. It doesn’t measure nutrients or pH.

What is the stuff floating on top?

Organic matter. It floats while the mineral particles settle, so measure only the layers on the bottom[4].

Can I use any jar?

Use a tall jar with straight sides and a tight lid. Straight sides keep each layer's height proportional to its volume.

Why is my result different from USDA's map?

USDA maps the soil typical of an area, at scales from 1:12,000 to 1:63,360[7]. Your sample comes from one spot in your yard.

Sources

  1. Colorado State University Extension, Estimating Soil Texture (GardenNotes #214)
  2. USDA NRCS, Soil Survey Manual (Agriculture Handbook 18), Ch. 3 “Examination and Description of Soil Profiles” (Soil Science Division Staff; eds. Ditzler, Scheffe, Monger; 2017)
  3. Ohio State University Soil Fertility Lab, Procedure for Soil Particle Size (Texture): 2-Hour Hydrometer Method (rev. July 2020)
  4. Washington State University Extension, Lewis County, Evaluating Your Soil Texture
  5. Colorado State University Extension, CMG GardenNotes #252, Worksheet: Soil Texture and Free Lime Lab (answer guide)
  6. Penn State Agricultural Analytical Services Laboratory, Particle Size and Sand Sieve Test
  7. USDA NRCS, Soil Survey Geographic Database (SSURGO), via Soil Data Access

Marko Visic · MPharm, BSc Physics · Last reviewed November 13, 2026

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