Soil Erosion Calculator (USLE)
The Universal Soil Loss Equation (USLE) is a widely used empirical formula for estimating average annual soil loss from agricultural fields and construction sites due to rainfall erosion. Developed by USDA-ARS researchers Wischmeier and Smith (1978), it is expressed as A = R * K * LS * C * P, where A is the predicted annual soil loss in tons per acre per year. Each factor reflects a different aspect of the erosion process: climate energy (R), soil susceptibility (K), terrain shape (LS), land cover (C), and erosion control practices (P). The Revised USLE (RUSLE2) is the current USDA standard with updated factor values.
USLE formula
A = R * K * LS * C * P
A = annual soil loss (tons/acre/yr)
Metric: A (t/ha/yr) = A (tons/acre/yr) * 2.2417
The USLE was developed from over 10,000 plot-years of erosion data. The Revised USLE (RUSLE2), maintained by USDA-NRCS, extends the method with improved factor equations and is the current regulatory standard for conservation planning in the US.
Interpreting USLE results
- Tolerable soil loss (T value) is typically 1 to 5 tons/acre/year for most US agricultural soils (NRCS).
- A predicted loss exceeding the T value indicates that erosion control practices are needed.
- The C factor is the most controllable: switching from bare fallow (C = 1.0) to no-till cover crops (C = 0.02) can reduce erosion by 98 percent.
- USDA RUSLE2 software (available free from NRCS) provides location-specific factor values and conservation planning tools.
- This calculator is educational. For regulatory compliance and NRCS conservation plans, use RUSLE2 or consult a certified NRCS soil conservationist.
Frequently asked questions
What is the Universal Soil Loss Equation (USLE)?
The USLE (A = R*K*LS*C*P) is an empirical model developed by USDA Agricultural Research Service to estimate average annual soil loss from sheet and rill erosion. A is annual soil loss (tons/acre/year), R is rainfall erosivity, K is soil erodibility, LS is slope length-steepness factor, C is cover-management factor, and P is support practice factor.
What is the R factor (rainfall erosivity)?
The R factor represents the erosive energy of rainfall and surface runoff. It is computed from 30-minute maximum rainfall intensity and storm energy. R values in the US range from about 50 in arid western states to over 500 in the Gulf Coast region. USDA provides R factor maps in the RUSLE2 database.
What is the K factor (soil erodibility)?
The K factor measures how susceptible a soil is to erosion by rain and runoff. It depends on soil texture, organic matter, structure, and permeability. K values range from 0.02 (very resistant soils) to 0.69 (highly erodible soils). Values for US soil series are in the USDA Web Soil Survey.
What are the C and P factors?
The C factor (cover-management) ranges from 0.001 (dense forest) to 1.0 (bare fallow). The P factor (support practice) accounts for erosion control practices like contouring (P = 0.5) or terracing (P = 0.1 to 0.6). Both factors reflect management decisions that significantly affect erosion rates.
What is the tolerable soil loss (T value)?
NRCS defines the tolerable soil loss (T) as the maximum annual rate of erosion that allows crop productivity to be maintained indefinitely, typically 1 to 5 tons/acre/year depending on soil depth and subsoil productivity. The NRCS Conservation Planner uses T values for erosion control planning.
Official sources
- USDA NRCS: NRCS Water Quality Conservation.
- USDA: Web Soil Survey (K factor data).
- USDA ARS: RUSLE2 Project.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.