ToolsGeotechnicalGround Stress & Earth Pressure

Earth Pressure Coefficient Calculator

Calculate Rankine active (Ka), passive (Kp), and at-rest (K0) earth pressure coefficients from friction angle. Includes Mayne & Kulhawy OCR correction for K0.

Last updated 1 February 2026

About this tool

Calculate the three fundamental earth pressure coefficients from the effective friction angle (φ'): active (Ka), passive (Kp), and at-rest (K0).

Ka and Kp use Rankine theory. K0 uses the Jaky (1944) formula for normally consolidated soils. Optionally enter the overconsolidation ratio (OCR) to estimate K0 for overconsolidated soils using Mayne & Kulhawy (1982).

These coefficients are the starting point for retaining wall design, basement wall loading, and any lateral earth pressure analysis.

How to use this tool

1. Enter the effective friction angle — φ' in degrees, from lab testing or published correlations.

2. Optionally enter OCR — overconsolidation ratio, if known, to get the OC-corrected K0.

3. Read Ka, K0, and Kp — multiply by σ'v to get lateral effective stress at any depth.

Technical information

Ka = tan²(45° − φ'/2) — Rankine active

Kp = tan²(45° + φ'/2) — Rankine passive

K0 = 1 − sin(φ') — Jaky (1944)

K0(OC) = K0(NC) × OCR^sin(φ') — Mayne & Kulhawy (1982)

Limitations

Rankine theory assumes a smooth, vertical wall with horizontal backfill. For inclined walls, sloping backfill, or wall friction, use Coulomb theory or log-spiral methods.

The Jaky K0 formula applies to normally consolidated soils. The Mayne & Kulhawy correction is empirical — for heavily overconsolidated clays, K0 can approach or exceed Kp.

Revision history

1 February 2026: Initial release

Disclaimer

This tool is provided for educational and general information purposes only. It is not a substitute for professional engineering advice, design or verification.

Diggy and its contributors are not licensed engineering consultants and no results generated by this tool should be used directly for construction, design or safety-critical decisions.

All values and outputs are based on published empirical correlations and should be independently checked and confirmed by a qualified geotechnical engineer before use.

By using this tool, you accept full responsibility for how you interpret and apply the information provided.

Spotted an error? Let us know.

Effective friction angle, φ' (°)

OCR — Overconsolidation ratio (optional)

Enter OCR > 1 to estimate K0 for overconsolidated soils (Mayne & Kulhawy 1982).

Related tools