How USSoilMap Works: Data Sources and Methodology

Every soil value on this site comes from a public US government source, USDA's soil survey, and every plain-language reading of it names the handbook or extension service it follows. This page shows which one, how we process it, and where its limits are. Every tool page also lists its own sources and the method behind its result.

Where your location comes from

Street addresses are located with the US Census Bureau Geocoder. It matches your address to street address ranges and places the point along that street segment, so the location is approximate, not a surveyed property point.^[1]

City names and ZIP codes use a single representative point for that place or ZIP Code Tabulation Area from the US Census Bureau's 2025 Gazetteer Files. That point can be far from your home, so these results are labeled "near the center" and you should click your exact spot.^[2]

Map clicks and "Use my location" use your coordinates directly. Before looking up soil, we round coordinates to three decimal places. That moves the lookup point by at most 0.0005 degrees: about 55 meters north–south, since a degree of latitude is about 69 miles, and less east–west.^[3]

Where the soil data comes from

Soil data comes from the USDA Natural Resources Conservation Service's Soil Survey Geographic Database (SSURGO), read live through USDA's official Soil Data Access service. SSURGO was built by the National Cooperative Soil Survey: soil scientists walked the land, described the soils and analyzed samples in laboratories.^[4]

USDA mapped this information at scales from 1:12,000 to 1:63,360. Each mapped area, called a map unit, usually contains one to three major soils plus some minor ones.^[4] What is a soil survey? explains how USDA's survey is made and how to read a map unit.

USDA refreshes the public soil survey database once a year. Every result shows its survey area and the date that survey's data was last updated.^[5]

How a point becomes your soil

We find the SSURGO map unit that contains your point and take the soil with the largest share of it, called the dominant soil. Its name and share are shown first, and the other soils in the map unit are listed below.

Soil properties come from that soil's surface layer: sand, silt and clay, organic matter, pH measured in a 1:1 soil–water mix, available water capacity, water held at field capacity (1/3 bar) and at the wilting point (15 bar), moist bulk density, saturated hydraulic conductivity, drainage class and hydrologic soil group.^[4][6][7]

For most properties USDA records a typical value plus a low and a high value. We show the typical value with the low–high range in brackets, exactly as USDA publishes them, and never average or extrapolate.

The soil profile shows every layer USDA records for the dominant soil, with its depths and texture. The soil order comes from the soil's classification in SSURGO, which follows USDA Soil Taxonomy.^[4][8]

How we name the texture

The texture class, such as loam or silty clay, is calculated from USDA's typical sand, silt and clay percentages. We apply the USDA texture class definitions from the Soil Survey Manual (Agriculture Handbook 18, 2017), the same boundaries as the USDA soil texture triangle.^[6][9]

USDA sorts mineral particles by size: sand is 2.0 to 0.05 mm, silt is 0.05 to 0.002 mm and clay is smaller than 0.002 mm.^[6]

When there is no soil to show

Some map units are mapped as non-soil areas, such as Urban land, Water or Rock outcrop. We show USDA's own name for these and never invent soil properties. If USDA lists a real soil inside that map unit, we show it separately as an associated soil, with a note that a developed site's surface may differ.

Points outside any surveyed map unit say so, and points outside the US and its territories are labeled as outside USDA coverage. If USDA's service does not respond, we say the lookup failed and offer a retry. A failed lookup is never shown as "no data".

What this data cannot tell you

SSURGO describes the typical soil of a mapped area. It is not a test of your yard, and the soil at a specific spot can differ, especially where soil was moved, filled or built on.^[10]

For fertilizer or lime decisions, use a lab soil test of your own soil, because SSURGO pH is a typical range, not your garden's current value. For construction, septic systems or anything with safety or legal consequences, get an on-site investigation by a qualified professional.

How we count states and shares

"States" means the 50 states plus the District of Columbia. US territories (Puerto Rico, Guam, the U.S. Virgin Islands, American Samoa and the Northern Mariana Islands) appear only in a table we label "states and territories"; the freely-associated states Micronesia, the Marshall Islands and Palau never appear in a US ranking. An in-state-share ranking (the share of a state's mapped soil that falls in one class) only includes states with at least 1 million classified acres, so a state with very little surveyed soil can't post a misleading share.^[4]

We use one denominator per measure, everywhere. A texture class's national share is its share of all acres that carry a USDA surface texture class (1,915.5 million acres, counted as described below); a soil order's national share is its share of all acres that carry a soil order. When a single state holds more than a third of a class's acres (Alaska alone holds about 36% of all silt loam acres), we also give the figure for the 48 contiguous states plus DC, so one outsized state doesn't skew the national number.^[4]

How we count soil-type acres

The acres, shares, ranks and top states on the soil type pages all come from one aggregation of USDA's survey. Each soil component in USDA's detailed soil surveys gets the texture class of its surface horizon, the first horizon below any organic (O) layer, using the sand, silt and clay limits of the Soil Survey Manual. Miscellaneous areas such as Urban land, rock outcrop and water are counted separately and not classified, and so are organic soils (Histosols), even where a mineral layer lies under their organic surface. A component whose surface horizon has no sand, silt and clay values also stays unclassified.^[4]

A component's acres are its map unit's acres times its representative percent. Summed across 3,386 detailed soil surveys, that is 2,077.9 million acres of soil components, of which 1,915.5 million carry a texture class. That classified total is the denominator for every texture-class share. Organic soils (Histosols) and miscellaneous areas get no texture class, so neither is in it; the soil types page gives their totals.^[4]

We name a specific soil series only when it has a published USDA Official Series Description. A map unit's component name that has no OSD page is left off rather than shown as a soil you can't look up.^[11]

Other values we show

Water table depth: for each map unit USDA reports the shallowest depth to a water table at any time of year, and separately for April–June. We show both.^[12]

Depth to bedrock: the shallowest depth to bedrock USDA records for the map unit, when present.^[4]

Flooding frequency: how often USDA expects the soil to flood. This is a soil-survey estimate, not a FEMA flood zone.^[13][14]

Farmland and land capability class: USDA's farmland classification (such as prime farmland, or prime only if drained) and the land capability class, non-irrigated and irrigated, shown exactly as published.^[15][16]

Shrink-swell: from each layer's linear extensibility percent (LEP), USDA's four shrink-swell classes are low (under 3%), moderate (3–6%), high (6–9%) and very high (9% or more). We show every layer and the highest class in the profile.^[17]

Soil suitability ratings

For septic systems and building sites, USDA rates each mapped soil in four classes. Not limited: features are very favorable, with good performance and very low maintenance. Somewhat limited: features are moderately favorable, and limitations can be overcome or minimized by special planning, design or installation. Very limited: one or more features are unfavorable, and limitations generally cannot be overcome without major soil reclamation, special design or expensive installation. Not rated: USDA does not rate this soil for that use.^[18][19]

Each rating lists the soil features behind it, such as depth to a saturated zone or slow water movement, each scored from 0 (not a limitation) to 1 (greatest negative impact on the use). Some states publish their own ratings using state rules, which we show alongside the national rating; the two can differ, and local approval follows the state's rules.^[18]

How we explain your results

The plain-language report ("What this means for you") turns these USDA values into short statements. Every statement is built only from USDA numbers and the fixed wording below (nothing is generated, averaged or invented), and each one links its source.

• Summary sentence: the drainage class, surface texture and surface pH, phrased against the 6–7 range most vegetables prefer.^[20]
• Soil pH (Oregon State University Extension): 6.0–7.0 is the vegetable range; 4.5–5.5 suits blueberries, azaleas and rhododendrons; values below 4.5 and above 7.0 are flagged. Every case notes that this is the mapped soil's typical value and a soil test shows yours.^[20]
• Soil texture (Colorado State and Oregon State Extension): the sandy, loamy, clay-loam and clay groups each get a one-line meaning.^[21][22]
• Water the soil holds (USDA available water capacity): each layer's available water capacity times its thickness, summed from the surface to 150 cm or a shallower limiting layer, named as USDA's class: very low (under 3 in), low (3–6), moderate (6–9), high (9–12), very high (over 12).^[7]
• How fast water soaks in (USDA Ksat classes): from saturated hydraulic conductivity: very low (under 0.01 µm/s), low (0.01–0.1), moderately low (0.1–1), moderately high (1–10), high (10–100), very high (100 or more), described plainly as very slow to fast.^[23]
• Lawns, houses and septic (USDA Building Site Development interpretations): USDA's own rating class and top limitations, national and, where published, state ratings.^[18][19]
• Foundation movement (shrink-swell / linear extensibility): low, moderate, high and very high.^[17]
• Rainwater runoff (USDA hydrologic soil groups, National Engineering Handbook Part 630 Chapter 7): groups A to D, and dual groups such as B/D where the first letter applies when the land is drained.^[24]
• Farmland and land capability: USDA's farmland classification and land capability class, shown as published.^[15][16]
• Soil order and series description (USDA Soil Taxonomy and Official Series Descriptions): a one-line description of the soil order, and USDA's own opening paragraph for the series.^[25][11]

Texture tools

Three tools find a soil's USDA texture class (the mix of sand, silt and clay) and all share one classifier, the USDA Soil Survey Manual boundaries written as rules in our code and tested on a 1% grid.^[6]

• Soil texture triangle calculator: enter sand, silt and clay percentages (from a lab or a jar test), or plot the soil USDA mapped at your address, layer by layer.
• Soil jar test calculator: settle a soil sample in a jar, measure the sand, silt and clay layers, and divide each by the total to get percentages.^[21]
• Soil ribbon test: estimate the class by feel, following Colorado State University Extension's texture-by-feel flowchart; it places a whole class, not exact numbers.^[21]

Maps and attribution

Map tiles come from OpenFreeMap, using map data © OpenStreetMap contributors. The map is drawn with MapLibre GL JS.

The map

The soil areas drawn around a point are USDA map unit polygons read live from Soil Data Access, clipped to the visible area and simplified to about 2 meters for display. You can color them by theme: the classes shown are USDA's own (soil type, drainage, flooding, farmland and hydrologic soil group), except the water-table depth bins, which are ours (we group USDA's shallowest annual water-table depth into "shallower than 25 cm", "25–50 cm", "50–100 cm" and "100–200 cm"). The satellite view uses imagery from USGS The National Map.^[4][12]

Data sources and licenses

Every dataset behind the site's figures, maps and lookups, from our data registry: who publishes it, the terms we use it under, how often it changes and when we last checked it. Each article cites the sources behind its own facts.