Free tool · USDA soil survey data, read by an excavation crew
Soil type by ZIP code
Enter a ZIP code or an address, or use your location. We pull the USDA soil survey for that spot and the ground around it, then turn it into what matters before you dig: how deep a patio base should be, and what to watch for with a retaining wall or a French drain.
The tool reads USDA-NRCS soil survey data (SSURGO) for 9 points: your point and 8 around it. It shows each soil’s drainage class, hydrologic group, clay, depth to bedrock and water table, plus NRCS digging and road ratings. It doesn’t replace a test hole on your lot.
Your address goes to the U.S. Census Bureau’s geocoder to find the point. We don’t see it or store it.
Your browser asks first. The coordinates go only to the USDA soil database, and we don’t store them.
Not sure? See frost line depth by state and ZIP code. It changes the patio base depth below.
Planning information, not a survey or engineering. Call 811 and check with your local office. Nothing you enter is saved: the lookups run in your browser.
How it works
A ZIP code uses the Census Bureau’s internal point for that ZIP code tabulation area (TIGERweb), plus 8 points 1 mile out in each direction. An address goes to the Census geocoder; your location comes from your browser. Address and location lookups sample your point plus 8 points about 250 ft away.
Each point is matched to a USDA-NRCS soil survey (SSURGO) map unit through Soil Data Access. For each map unit we show the dominant drainage class and hydrologic group, the shallowest bedrock and water table, and flooding. Details come from the largest named soil in the map unit.
Classes and ratings are NRCS’s. The patio base depth uses the Concrete Masonry and Hardscapes Association’s base rule. Wall and drain notes come from Allan Block and NDS installation guidance; where a note is our own read, it says so. The ZIP center isn’t always the town center, and points can land outside the ZIP or in water.
What the soil terms mean
| Term | What NRCS means | Why it matters for a build |
|---|---|---|
| Drainage class | How fast water leaves the soil, from excessively drained to very poorly drained. Poorly drained soil is wet at shallow depths periodically or for long periods. | Wet ground is one of the conditions the CMHA adds patio base for, and it puts water behind walls. |
| Hydrologic soil group | A to D by how fast water soaks in when the soil is thoroughly wet. In a dual group like B/D, the first letter is for drained areas and D is for undrained. | Whether a dry well or rain garden can soak water in. |
| Depth to bedrock | Shallowest depth to bedrock among the soils that make up 15% or more of the map unit. | Rock limits trenches, footings and wall bases. |
| Water table | Shallowest depth to a saturated zone at any time of year, among the soils that make up 15% or more of the map unit. A saturated zone that lasts less than a month doesn’t count. | A drain or base below it sits in groundwater. |
| Frost action | Likelihood of frost heave from ice lenses, and loss of strength when the soil thaws. Silty and clayey soils with a high winter water table are the most susceptible. | Heave and thaw weakness damage pavements and slabs. |
| Flooding and ponding | Chance per year of overflow from streams, runoff from nearby slopes or tides (flooding), or of standing water in a closed low spot (ponding). | Outlets and patios in low ground. |
The two NRCS ratings we show
| Rating | What NRCS rates | How we use it |
|---|---|---|
| Shallow excavations | Trenches or holes dug to a maximum depth of 5 or 6 ft: ease of digging and resistance to sloughing (bedrock, large stones, dense layers, water table, flooding, ponding, slope, texture, shrink-swell). | Footings, wall base trenches and drain trenches. |
| Local roads and streets | All-weather roads on a cut or fill subgrade with a gravel or stabilized base: ease of excavation and grading, and traffic-supporting capacity (soil strength, shrink-swell, frost action, water table). | The closest NRCS rating to a driveway or patio base. |
Not limited means the soil has features very favorable for the use: good performance and very low maintenance. Somewhat limited means the limits can be overcome or minimized by special planning, design or installation: fair performance and moderate maintenance. Very limited means one or more features generally can’t be overcome without major soil reclamation, special design or expensive installation: NRCS expects poor performance and high maintenance.
Patio base depth by soil
The CMHA gives 4 in. of base for patios and walks and 6 in. for residential driveways on strong, well-draining ground in a non-freezing climate, then adds 50% of that minimum for each condition your site is missing.
| Conditions your site is missing | Patio or walk | Residential driveway |
|---|---|---|
| None | 4 in. | 6 in. |
| One (weak subgrade, poor drainage or freezing) | 6 in. | 9 in. |
| Two | 8 in. | 12 in. |
| All three | 10 in. | 15 in. |
The CMHA’s own example is a driveway missing all three conditions, which it calls a rough guess of 15 in. (6 + 3 + 3 + 3). The tool counts wet soil from the NRCS drainage class (somewhat poorly drained or wetter), a weak subgrade from NRCS low strength or subsidence on the road rating, and freezing from your answer above. Those cutoffs are ours, not the CMHA’s.
Questions
How do I find out what type of soil I have?
Enter your ZIP code or address above. The tool reads the USDA-NRCS soil survey (SSURGO) for that spot and 8 points around it and lists the soils mapped there, with drainage class, hydrologic group, clay, depth to bedrock and water table. For one exact parcel, draw it in USDA’s Web Soil Survey. Before you build, dig a test hole: the survey is a map, not a test of your lot.
How accurate is a soil map by ZIP code?
It’s a starting point. NRCS collected SSURGO at map scales from 1:12,000 to 1:63,360, and each map unit is a mix of soils, which is why we show the main soil’s share. A ZIP lookup samples the center point of the ZIP code area and 8 points 1 mile out, so it describes the general area, not your yard. Fill, grading and old construction can change what’s on your lot.
What does poorly drained soil mean?
It’s an NRCS drainage class. In the Soil Survey Manual, poorly drained soil is wet at shallow depths periodically during the growing season or stays wet for long periods, and free water at shallow depth is common. Somewhat poorly drained soil is wet at a shallow depth for significant periods. Very poorly drained soil has free water at or near the surface during much of the growing season.
What is a hydrologic soil group?
NRCS puts soils in groups A to D by how fast water soaks in when they’re thoroughly wet. Group A takes water in fast with low runoff, B at a moderate rate, C slowly, and D very slowly with high runoff. Group D soils are chiefly clays with high shrink-swell, soils with a high water table, soils with a clay layer at or near the surface, and shallow soils over nearly impervious material. A dual group such as B/D means B where drained and D as it is.
How thick should a paver base be on clay or wet soil?
The Concrete Masonry and Hardscapes Association starts with 4 inches of base for patios and walkways and 6 inches for residential driveways, on strong, well-draining soil in a non-freezing climate. For each of those conditions your site doesn’t have, it adds 50% of that minimum. A patio on wet soil where the ground freezes works out to 4 + 2 + 2 = 8 inches. The tool does this math with the soil it finds.
Will a French drain work in clay soil or with a high water table?
Sometimes, with limits. NDS, a drainage products maker, says clay-heavy soils may need additional solutions, such as a deeper and wider trench, and that when the problem is a high water table or seasonal groundwater, a French drain may give only temporary relief. Either way the pipe needs slope and a safe place to send the water, such as a storm system or lower ground.
Can you build a retaining wall in clay soil?
Usually, with more care. Allan Block says clay soils put more pressure on a wall than sandy soils because they hold moisture and may need more reinforcement, and that heavy clays and organic soils are unsuitable in the reinforced zone and should be removed and replaced. It recommends a qualified geotechnical engineer for an accurate soil classification. Check your state’s permit height for walls too.
Sources: USDA-NRCS Soil Data Access (SSURGO), queried live; USDA-NRCS, Soil Survey Geographic Database (SSURGO); USDA-NRCS Web Soil Survey attribute and rating descriptions; USDA Soil Survey Manual, Ch. 3, drainage classes (pp. 213–215); U.S. Census Bureau TIGERweb, ZIP code tabulation areas; U.S. Census Bureau Geocoder; CMHA, Proper Concrete Paver Base and Depth (May 23, 2025); Allan Block, Retaining Wall Soil Requirements; Allan Block, Best Practices Ch. 3: Water Management; NDS, What Is a French Drain. Last checked November 12, 2026.
Related: frost line depth by state and ZIP, the drainage guide, the French drain calculator, soil types in Pennsylvania, drainage laws by state and retaining wall permits by state.
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