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USCS soil classification calculator (ASTM D2487)

Enter percent passing the No. 4 and No. 200 sieves, D10, D30 and D60 (typed or computed from your gradation), and the liquid and plastic limits. The calculator returns the group symbol, the basic group name, each decision in plain words, and plots the fines on the plasticity chart.

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Key takeaways

  • Fewer than 5 % fines: GW, GP, SW, SP. More than 12 %: GM, GC, SM, SC. 5 to 12 %: dual symbols.
  • GW needs Cu ≥ 4 and 1 ≤ Cc ≤ 3; SW needs Cu ≥ 6 and 1 ≤ Cc ≤ 3.
  • Fines above the A-line, PI = 0.73 × (LL − 20), are clays; below it, silts.
  • Full group names with modifiers follow the complete D2487 charts.

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How it's calculated

How is the result calculated?

Coarse if more than 50 % is retained on No. 200; Cu = D60 ÷ D10, Cc = D30² ÷ (D10 × D60); A-line PI = 0.73 × (LL − 20).

  1. 01Coarse-grained: more than 50 % retained on the No. 200 sieve. Fine-grained: 50 % or more passes the No. 200 sieve
  2. 02Gravel: more than 50 % of the coarse fraction retained on No. 4. Sand: 50 % or more of the coarse fraction passes No. 4
  3. 03Fewer than 5 % fines: GW, GP, SW or SP. More than 12 %: GM, GC, SM or SC. 5 to 12 %: dual symbols such as GW-GM or SP-SC
  4. 04Cu = D60 ÷ D10 and Cc = (D30)² ÷ (D10 × D60). GW: Cu ≥ 4 and 1 ≤ Cc ≤ 3. SW: Cu ≥ 6 and 1 ≤ Cc ≤ 3
  5. 05A-line: PI = 0.73 × (LL − 20). U-line: PI = 0.9 × (LL − 8)
  6. 06LL < 50: CL if PI > 7 and on or above the A-line; ML if PI < 4 or below the A-line; CL-ML if 4 ≤ PI ≤ 7 on or above it. LL ≥ 50: CH on or above, MH below
  7. 07Organic (OL or OH) when oven-dried LL ÷ undried LL < 0.75. Peat (Pt) is identified visually

Rounding: moisture content, liquid limit, plastic limit and plasticity index to 0.1. Full precision is kept between steps.

FAQ

Frequently asked questions about the uscs classification calculator

Does the calculator give the full group name?

No. It gives the group symbol and basic group name. Full names with modifiers such as "with sand" or "with gravel" follow the complete current ASTM D2487 charts.

Can I compute D10, D30 and D60 from my sieve data?

Yes. Enter openings in mm and percent passing; the calculator interpolates on a log scale between the sieves that bracket each value. It will not extrapolate beyond your data.

What happens with 5 to 12 % fines?

The soil gets a dual symbol, such as SW-SM. When the fines plot as CL-ML, the calculator uses the clay symbol and asks you to confirm with the full D2487 chart.

How is organic soil identified?

Enter the oven-dried liquid limit. If it divided by the undried liquid limit is below 0.75, the soil is organic, OL or OH. Peat is identified visually.

What units should D10, D30 and D60 use?

Any single length unit, because Cu and Cc are ratios. The gradation table uses millimeters.

Related guides and pages

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Sources and further reading

Standards are summarized in our own words. Read the current edition from the publisher before you test.

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