What soil texture is and why it matters
Soil texture describes the mix of three mineral particle sizes in your soil: sand, silt and clay. The USDA defines the size ranges in millimeters, and every mineral soil is some combination of the three, always adding up to 100%.
| Particle | Size range | Feel |
|---|---|---|
| Sand | 2.0–0.05 mm | Gritty, individual grains visible |
| Silt | 0.05–0.002 mm | Smooth, flour-like when dry |
| Clay | Under 0.002 mm | Sticky and plastic when wet |
Texture matters for irrigation because it sets two things at once: how much water the soil can hold where plant roots can reach it, and how fast water can move into and through the soil. A sandy soil and a clay soil can receive the exact same watering schedule and behave completely differently, one draining before roots can use much of the water, the other ponding or running off before it soaks in.
The soil and water quality calculators use texture as a starting point for several other estimates. Once you know your class here, the available water capacity calculator and the soil infiltration rate calculator take it further for a specific root zone depth or measured intake test.
How this soil texture calculator works
The calculator turns your sand, silt and clay percentages into a point on the USDA soil texture triangle, then reports the class that point falls in along with typical water properties published for that class.
1. Getting to sand, silt and clay percentages
From sand and clay
Silt % = 100 − Sand % − Clay %
Sand and clay are the two percentages most lab reports and feel tests give directly; silt is the remainder, so the three always sum to 100%.
From a jar test
Sand % = Sand layer height ÷ Total settled height × 100
The same formula applies to the silt and clay layers. Because it's a ratio, any consistent length unit works, and unit conversion isn't needed.
2. Classifying the texture
The three percentages are checked against the boundary lines of the USDA soil texture triangle, which defines 12 classes from Sand through Clay based on where sand, silt and clay percentages fall relative to one another. The boundaries used here follow the triangle published in the USDA-NRCS Soil Survey Manual and reproduced in the NRCS Soil Texture Calculator.
Two worked examples below show the logic step by step, and both were checked by hand against the calculator's own output.
3. Typical water properties for the class
Available water capacity
Reported as a range in inches of plant-available water per foot of soil depth (or mm per meter, in metric), grouped by texture following USDA-NRCS field guidance on estimating soil moisture. It's a typical range for the class, not a measurement of your soil.
Basic infiltration rate
A representative steady-state rate in inches per hour (or mm per hour), based on Rawls, Brakensiek and Saxton (1982). Real infiltration on your site also depends on structure, compaction and slope, so treat this as a starting point rather than a field measurement.
When this calculator isn't the right tool
It classifies the mineral fraction of a soil sample. Use a different approach for:
- Potting mixes and soilless media, which are mostly organic material and fall outside the USDA triangle. See the available water capacity calculator instead.
- A measured infiltration or intake rate for your actual field, rather than a typical value for the texture class. Use the soil infiltration rate calculator with your own catch-can or ring-infiltrometer data.
- Current soil moisture or a watering deficit, which changes day to day. See the soil moisture calculator or the soil water balance calculator.
- Engineering classification for foundations or septic design, which uses different systems (such as USCS) alongside texture. Consult a geotechnical professional for that work.
Soil texture calculation examples
A gardener runs a jar test: after shaking sifted soil with water and letting it settle through the timed stages, the sand layer measures 3 in, the silt layer 1.2 in and the clay layer 0.8 in.
- Total settled height: 3 + 1.2 + 0.8 = 5.0 in.
- Sand: 3 ÷ 5.0 × 100 = 60%.
- Silt: 1.2 ÷ 5.0 × 100 = 24%.
- Clay: 0.8 ÷ 5.0 × 100 = 16%.
- Triangle check: clay is under 20%, sand is 60% (over 52%), so the point falls in Sandy Loam.
- Typical properties: about 1.3–1.7 in/ft available water capacity, and a representative infiltration rate of about 1.02 in/hr.
The same method with lab percentages, in metric units
A soil test lab reports 40% sand and 20% clay for a sample (silt is the remainder):
- Silt: 100 − 40 − 20 = 40%.
- Triangle check: clay is 20% (7–27% range), silt is 40% (28–50% range) and sand is 40% (23–52% range), so the point falls in Loam.
- Available water capacity: about 1.5–2.1 in/ft, converted to about 125–175 mm per meter of soil.
- Infiltration rate: about 0.52 in/hr, converted to about 13.2 mm/hr.
Both examples match the calculator's own output for the same inputs. Near a boundary, a small change in sand or clay can shift the class, which is one reason to treat a jar-test result as an estimate rather than a lab-grade figure.
How to run a jar test
The jar test is a simple, low-cost way to estimate texture without a lab. Clemson Cooperative Extension's Home & Garden Information Center describes the standard timed version:
- Sift the soil through a mesh sieve or old colander to remove debris, roots and large organic matter.
- Fill a straight-sided jar about a third full of the sifted soil, then top it up with clean water, leaving some space at the top.
- Cap and shake vigorously until the mixture is a uniform slurry. A small amount of dishwasher detergent added first helps keep the particles from clumping back together.
- Set on a level surface. After exactly 1 minute, mark the top of the settled layer: this is sand.
- Leave for 2 hours, then mark the next layer up: this is silt.
- Leave for a total of 48 hours from the start, then mark the final layer: this is clay, settled on top of the silt.
- Measure the height of each layer and the total height with a ruler, then enter them above.
Reading a layer too early or too late is the most common source of error, since the sand/silt boundary depends on the 1-minute mark and the silt/clay boundary depends on the full settling window. A kitchen timer for each stage makes the readings much more repeatable.
What can throw off the result
The classification itself is just triangle geometry, but the percentages you feed it are only as good as the sample and method behind them.
| Factor | Effect on the result | What to adjust |
|---|---|---|
| Organic matter | Organic particles can settle with or near the silt and clay layers, inflating those readings. | Sample from a few inches down, below most of the organic-rich topsoil, or use a lab test on high-organic samples. |
| Undispersed clay | Clay that clumps instead of dispersing can settle early and get miscounted as silt or sand. | Add a dispersant such as dishwasher detergent and shake until fully mixed. |
| Reading layers off-schedule | Sand and silt boundaries are time-dependent; early or late readings shift the split. | Time the 1-minute and 48-hour marks precisely. |
| Gravel and coarse fragments | The USDA triangle covers only particles under 2 mm. | Sieve out gravel and rock before filling the jar. |
| Sampling depth and location | Texture can vary noticeably across a yard or by depth. | Test multiple spots or depths separately rather than mixing samples from very different areas. |
| Salts and water quality | Very saline or sodic samples can disperse or flocculate unpredictably. | For known saline soils, use a lab analysis instead of a jar test. |
Frequently asked questions
What is soil texture and why does it matter for irrigation?
Soil texture is the mix of sand, silt and clay particles in your soil, and it's one of the biggest factors in how water behaves once it hits the ground. Sandier soils let water move through quickly and hold less of it for plants to use, while soils with more clay hold more water but let it in and drain it more slowly. Knowing your texture class helps you set realistic watering depths, run times and schedules instead of guessing.
How do I find my soil's sand, silt and clay percentages?
Two common ways: a jar test you can do at home, or a laboratory particle-size analysis. For a jar test, shake sifted soil with water in a straight-sided jar, let it settle in timed stages, and measure the height of each layer. A lab test uses sieves and a hydrometer to measure the percentages directly and is more precise, especially near a class boundary.
See how to run a jar test above, or check current soil moisture with the soil moisture calculator once you know your texture.
How accurate is a jar test compared to a lab texture analysis?
A jar test is a rough field estimate, not a lab measurement. Organic matter, incomplete dispersal of clay particles and reading the layers at the wrong time can all shift the result. It's good enough to tell a sandy soil from a clay soil and to get a starting texture class, but if your result sits close to a class boundary, a laboratory hydrometer or sieve analysis will give a more reliable answer.
What does it mean if my soil is classified as loam?
Loam sits in the middle of the texture triangle, with roughly balanced sand, silt and clay. USDA NRCS field guidance on estimating soil moisture lists a typical available water capacity of about 1.5 to 2.1 inches per foot for medium-textured soils like loam, and a representative basic infiltration rate for loam of about 0.52 inches per hour, based on Rawls, Brakensiek and Saxton (1982). In practice that usually means loam holds a useful amount of water for plants and takes in water at a moderate, manageable pace.
How does soil texture affect how often I should water?
Texture sets both how much water your soil can store for plants and how fast water can soak in without running off. Sandy soils have lower available water capacity, so they typically need smaller, more frequent waterings. Clay soils hold more water but take it in slowly, so they often do better with longer intervals and shorter, split run times to avoid runoff. This calculator shows the typical numbers behind that pattern for your texture class.
Can two soils with the same texture class behave differently?
Yes. Texture class only describes the mineral particle-size mix. Organic matter content, soil structure, compaction and rock fragments all affect how water actually moves and how much a soil holds, even when two soils share the same sand, silt and clay percentages. Treat the texture class as a starting point, not the full picture.
Does this calculator work for potting mix or soilless growing media?
No. The USDA texture triangle classifies mineral soil particles under 2 mm and doesn't apply to bark, peat, coir or other soilless components used in container mixes. For container and raised-bed watering, the available water capacity calculator is a better starting point.
See the available water capacity calculator or the container plant watering calculator.
Can soil texture change over time?
The sand, silt and clay percentages themselves change very slowly, mainly through erosion, deposition or deliberately mixing in large amounts of sand or clay. What changes much faster is soil structure: how those particles clump together, which is affected by organic matter, tillage, compaction and biological activity. Structure, not texture, is usually what improves with better soil management.
What's the difference between soil texture and soil structure?
Texture is the fixed mineral makeup: the proportions of sand, silt and clay. Structure is how those particles are arranged and bound into aggregates, which is shaped by organic matter, roots, worms and how the soil is managed. You can improve a soil's structure with compost and reduced compaction, but you can't practically change its underlying texture class.
Who built and checked this calculator
Licensed Professional Engineer and Irrigation Association Certified Irrigation Designer with more than 20 years in irrigation design, system auditing and landscape water management. Full profile
How this page was checked
- The triangle classification was traced by hand for both worked examples and matched against the calculator's output.
- Available water capacity and infiltration figures are taken directly from the sources below, not estimated.
- Boundary logic was tested against reference points published by USDA and university sources.
Sources
- USDA Natural Resources Conservation Service. Soil Survey Manual (USDA Handbook No. 18) — USDA textural triangle and class boundaries.
- USDA Natural Resources Conservation Service. Soil Texture Calculator — reference implementation of the texture triangle.
- USDA Natural Resources Conservation Service. Estimating Soil Moisture by Feel and Appearance — available water capacity ranges by texture group.
- Rawls, W.J., D.L. Brakensiek and K.E. Saxton (1982). Estimating Soil Water Properties. Transactions of the ASAE. [VERIFY URL] — basic infiltration rate by USDA texture class.
- Clemson Cooperative Extension, Home & Garden Information Center. Soil Texture Analysis: The Jar Test — jar test procedure and timing.